@Takkie: Sounds like Red Rover?

So I know this isn't an original idea, but I always loved the Assault game mode in UT and it would be awesome to see it realized in Q3. The main reason I like it is because there's so much variety that you can implement in the map and objective design. There's potential for some neat maps based on id software game stories, like a Wolfenstein-themed Assault map where the attacking team tries to infiltrate a Nazi stronghold, or a Doom-themed Assault map set on Mars where the attacking team tries to destroy the portal to Hell before it opens while the defending team protects it so it can open. There's even potential to tap into the lore of original Quake 3 characters, like Keel and the Spiker Insurrection, or the war between Hunter and the Sorg (Sorlag's race). Assault maps are a great way to mix storytelling with arena FPS combat which makes them so cool in my opinion.

@muffinator I had to Google red rover and in the Netherlands we call it 'overlopertje' which translates to 'turner' or 'crossover'. 'Red rover' would be an appropriate name for game type because it has similarities, yes. :)
Edited 10.57 hours after the original posting.

T10}) the idea is bassicly that you can scroll through your ammo inventory like you can scroll through your weapon inventory. So weapon and ammo are not connected to each other anymore. There are different combinations possible. The ammo changes the way each weapon works. So here are some examples.
When you select ammo 'bullets' this will mean that all weapons will consume the 'bullets ammo' type and upon firing the firing rate of every weapon is increased significantly.
When you select 'shells', multiple bullets, rockets, rails, plasma etc will be fired at once with significant spread. (a shotgun effect for all weapons).
The ammo 'grenades' will make bullets, rockets etc do damage on impact and explode some time later with additional damage.
The 'lightning' ammo will send an extra electric charge and the target gets charged. This charge will consume health and will deplete over time (like an electric poison) The bullets, plasma balls, rockets can have additional electric effect on them.
When firing a weapon with the ammo 'cells' this will cause extra splash damage to the weapons fire impact. A plasma effect on fired ammo might be appropriate.
Selecting the 'rocket' ammo will cause all bullets, shells etc. to explode on impact and give some extra splash damage.
Ammo 'slugs': all weapons firing impact instantly (or increased velocity), without spread (or much less) and plasma balls are smaller, all weapons also have longer reload times.
The Bfg ammo 'plasma': damage from all the weapons increased, longer reload times, significant addition of splash damage...
The ammo selection can be bind to a key (or mouse wheel). The ammo will be consumed as normal and you can pick it up as normal.
So it is just another game setting...
I edited this idea, I think this way it is much easier to implement and it is much more versatile in usage. And more fun.
Edited 3.83 minutes after the original posting.
Edited 5.96 days after the original posting.

Sorry, haven't tried it yet, but I would suggest the following configuration:

• it only pushes upward when player is moving up (think of real life, where you can do this but only when momentum is upwards)
• speed of extra push upwards depends on the vertical speed (like in real life).
• zero vertical speed bounces you horizontally only (imagine you jump towards a wall 1 meter away, if you hit it when you have zero vertical speed, push would return you exactly to where you began).
• it can work when you are falling to, but never to reduce vertical speed (like in real life).

So you could climb up through two walls only when they are close enough.
(other games are using wall jumping! like Apex: www.youtube.com/watch)

Regarding my other suggestion, about a relative gravity mod (up-down is player-specific), not sure if possible but I envision the mod where you can easily change the "direction" of gravity using for instance the Shift key. So you are playing normally and want to grab an item which is for instance in the "cealing", you do Shift+E (E being the key for forward), and that flips the gravity of the player 180 degrees. Same with 90 degrees left or right, using Shift+S and Shift+F. You can imagine this being hugely versatile (but also very dizzying) by adding an entirely new dimension to the spacial strategy of the game. Only problem is the GL, which is gravity-specific, so needs to be decided how it would work with player-specific gravity.

And I'm being a leecher here, sorry. Don't have the skills nor the time to help beyond ideas and some testing once in a while. But anything that comes through is welcome! Btw, good to see so many ideas but more than a single mod, what this might end up being is a whole collection of new mods. You could call it "The Last Mod" or "The Ultimate Mod".
Edited 6.48 minutes after the original posting.

In hindsight T10)
This could just be a game type where besides scrolling through the weapon selection you can also scroll through ammo selection giving a wide range of combination as described, without having to 'levelup'. Edited T10 accordingly.
Also I edited T8 with a model suggestion for the obelisk.
Edited 1.34 hours after the original posting.

T11) "hot potato"
Inspired by the 'catch the chicken' mod this idea is the sort of opposite.
Everybody has normal weapons except for one unlucky player. This player spawns with the Bfg (hot potato). With this gun you cannot score. When you hit another player with the bfg this player gets the bfg and cannot score. So basically you want to avoid getting the bfg and for the rest everything is the same. Several options are possible for example in TDM or larger FFA games you could have multiple 'hot potatoes'. Or the player with the hot potato can (or cannot) be fragged. Perhaps an instagib version...
Edited 8.11 hours after the original posting.
Edited 9.82 hours after the original posting.

T12) I think this could be very fun for 1v1, TDM, CA or even CTF: imagine a map divided in two balanced zones (could be symmetric but do not need to). One is colored blue and the other red, each individual/team asigned to one color. The beginning of the zones are indicated with a "laser-type of visible layer". In the middle of the map there is a small neutral area with important items (e.g. powerup, MH). The key is this: when you enter into another player's zone, you start to lose health and armor (receive damage). That means you need to armor well before going out of your zone or entering another player's zone.
The advantage of this mode is that it lowers the propensity to overrun your enemy after killing them and gaining item control. It makes the game more strategic but also more focused on aim.
Such propensity for dominance could be countered even more by restricting item pickup by teams/zone.
What do you think?

@raspatan I like it.
Might be cool if it was sort of weapon so you can 'paint' your area and if others enter it they recieve damage. This way the area is flexible and under command of the players. You could set the max amount of 'paint' (per team or player) and if you paint more, the oldest 'paint' will be removed. This way you can set up little traps... Hmm a bit like the proximity launcher from TA

@Takkie sounds one way to implement it, provided as you say there is a fixed amount of paint you can do, otherwise overrunning enemy becomes easier. You could also set up a timer for each painted zone. And if you go full fornite, you can then do the zones reduce in size... hey... Quake 3 Fortine Arena on the horizon?

I believe this is sort of already built in to OA. I know you can replace weapons, but I don't think you can move them around. Speaking of which, compatibility with OA would be great.
Edited 53 seconds after the original posting.

Another idea I have been thinking about recently is a modification of One Flag.

Instead of a neutral flag that is brought to the enemy base, make a central specific spot, that when the player is standing in, it will gradually convert the flag to their team color, something like 10% conversion every two seconds or something. A visual flag color change would be helpful too, gradually changing the flag color from blue to red and vice versa. Kind of similar to RegenCapture mode in Sauerbraten. Both bases will have access to the area to convert the flag, and once converted, it can be brought to the appropriate base to score a point. However, if captured by the enemy team, it first must be converted to the appropriate team color.

@themuffinator if you want it I'd be more than happy to to share the source code of 'The Dead Simple' (TDS) mod with you to integrate it with 'level up'.
I think that it can add a lot of versatility to the mod. Because most of the ideas discussed here are gametype and weapon modification related and TDS is more about organizing different styles of gameplay.