Mhh, new features... I don't need better graphics but every wannabe gamer these days want's that and much blood. So to attract people you need at least this. As for my own preferences.
I wan't a better select map menu with filters and best time display and such. Player collision with own rocket projectiles. Projectiles going through portals. Optional airjump/walljump. Grappling hook with better physics (almost like http://www.moddb.com/mods/tension)
Would be cool to have a cfg tool where especially new players can change their settings and understand what this changes do to the game (maybe with a explanation of the cvars). I think its much to hard in q3 defrag for new players to know all these stuff q3 comes with and so they quit playin the game. The oldshool players who knew all this stuff are in much better position to set up the game so it would be great to have the same possibilitys for newbies.
A good serverbrowser is also important. Maybe it is possible to link the game with a webpage like q3df to join a server directly from the serverlist of this page?
This might be obvious, but online defrag is very lame without flawless client prediction / antilag, this should be priority #2 after physics. Team defrag modes require it, so there is some extra incentive.
Being able to easily define mouse input behavior beyond basic sens/accel would be great, though it might make cheat detection less simple.
Additive rather than subtractive map design could be a valuable change, and of course the df2.0 map features are worth including.
Of course the only sane map solution, for trickjumping at least, is to allow anyone to make them. Have any submission criteria you want, just let everyone make maps and play them without excess hassle.
Oh, you specified features other than movement physics, but it must be said: The current defrag movement is the minimum standard of refinement and skill expression. Do not listen to anyone who tells you that it is too complicated or difficult, it isn't. "Noob-friendly" features such as sprint, auto-accel, auto-jump, etc are completely indefensible. Different can be good, to almost any extent, but change for the "benefit" of the lazy or unwilling at the expense of the interested and capable is criminal.
UT2003 was fun for tricks. But the developers removed the possibility to combine 2 strongest trick jumps (and get an extra cheat-like jump) because it was excessive in the game. Some players learned to make those combos and fly over any gap on any map.. Plus walljumps etc, the shooter part was (too) antsy in UT2003. Although some players (me too) do like it, it better suits for tricks than for fight modes.
Similar thing with Warsow. It took much from CPMA. Although it does not have OBs and gazboosts, its extraordinary effecient walljumps and ramp slides do their business. It is fun to jump around the maps, find new tricks and shortcuts of different difficulty, BUT the shooting part became even more antsy. When you fire a rocket up and may have an air rocket, your opponent suddenly makes a walljump midair and avoids your rocket. That is very disappointing. Also, who needs multiple rocketjumps in freestyle, if you can just reflect your speed to any direction (even turn 180degrees) instanly, on any floor or at any wall. Yeah, there's a special bound key for that. Warsow teleporters save the speed, but reset the direction of that speed. This is useful in Race (Defrag-like mode in Warsow), but in shooter modes it is often excessive. Imo, tricking in Warsow is suitable for straferuns and tricks on casual fight maps. But not for weapon runs / freestyle tricking. Shooter modes in Warsow are fun, but CPMA is still more fun and more serious.
The point here is: tricks are interesting, but in shooters you gotta shoot your enemies. The balance is important. To me, the best trick/shoot balance I've seen is there in CPMA. Easy to jump/move across the map, almost no limits for improvement there, AND it is still easy enough to aim and get frags. Vq3 and QL are easier to aim, but the movement is not that fluent.
What for map objects,
Xonotic has a nice type of portals:
Not only projectiles fly through them, but also rails and any other weapons/items.. A player can stand 1 left leg in 1 place, and right in another. These teleporters save the velocities vectors (as in Portal and similar games). And this may be cool in some map designs/layouts. But not all the teleporters should be such. Q4 shootable teleporters showed that this can break the gameplay sometimes. For instance, Aerowalk is unplayable with rockets/grenades flying through teles.
Portal and Portal 2 have many options for tricking. Nexuiz had that type of teleporter guns, to put entrance and exit of teles whereever you want.. But it breaks the rules of the game. If you put a tele between RA and MH, you can control them both - not fair, not interesting. The more specific tricking weapons you add (teleporter shooter, paint shooter etc) - the more complicated gameplay is. And the farther from FPS it gets, closer to puzzle/maze game.
Grenades bouncing on jumpads are not new. They do bounce in Warsow, there were such in q4 if I recall, there's nothing interesting in it.
Do not make RJ extra strong as in Nexuiz - its lame. Do not allow simple +forwardkey speed gain - dumb. Do not make special weapon for a mid-height RJ with little damage (UT2003/UT2004/Warsow/Nexuiz) - this is stupid and not usable.
To me, it is very important how weapons sound. I love the sounds of rocket launchers in Q4, Nexuiz and Xonotic. On the opposite, the rocket shot in Warsow is so annoying, loud and hard to listen.. And the gauntlet in Warsow sounds just funny
A savepos is very important for training tricks. A versatile hud is very important.
It would be interesting if players could push one another. If I could push a camper's back to make him fall from an edge.. Not only that. I mean the law of conservation of momentum. I haven't seen it in any games yet. When I'm strafejumping at, say, 600 ups, and I hit another player's back, who is strafejumping at 500 ups - the result is I stop to zero, the other player doesn't even know I touched him. Would be nice if I push him and we both continue jumping at 550 ups.
Last but not at least, such a new game definitely needs a comprehensive tutorial (preferably video) for all the types of tricks.