Yes, the look should definitely be carefully orientated at what we have already, avoiding a random mixture of styles (see nexuiz' random collection of player models here). I would like to see that the models differ slightly from each other, when the weapons itself do, due to tweaked vars. So nothing that is too similar to modern arsenal of these days (though most SF weapons are roughly orientated at modern weapons).
Getting the look right is not easy, I agree here, but I found concept art being a great help for that.
(slightly offtopic: any concepts for a new player model would be also welcome. Just be prepared that it will be discussed mercyless by community.)
And where concept art helps for 3d modelling, it maybe also helps for weapon tweaking! So I end this with some random ideas:
High-range SMG:
-Alt-Fire is scoped (less than rifle though)
-shoots semi-auto 1 bullet per click
-damage.. subject to balancing, my guess is 1.5x could work
Auto Shotgun:
-Alt-Fire doesnt ricochet anymore, but empties the clip rapidly in full-auto style (and begs for weapon jam even more than default shotgun)
Plasma:
-many possibilities here:
-different effects could be displayed by slightly different plasma colours/textures (is there a texture at all in it?), for example healing (the idea to make it similar to linkgun from UT2004 was meantioned somewhere already)
-instead of creating a cloud it could make a beam (start/end points determined by player position when he starts/ends charging, or it creates kind of freehand path determined by player movement while he charges)
-plasma trap: player charges a ball, but it is compressed (either invisible or a really small piece of plasma), and other players hear a sound when they are in range (similar to charging sound, but different from that). If they get even closer, the trap deflates to a ball and "shows the light".
Different side weapons:
That is a bit different thing now.. there could be a choice of side weapons, and players can set in there settings (or before each match) what side weapon they wanna have.
Alternatives to pistol could be:
-healing "thingy" (a miniature version of plasma gun, specialised in healing, maybe able to deal little damage too), also makes player immune to burn/bleed
-radar device (switch radar off by default, enable it again when wearing this tool)
-knife
-grenades (take them off the map and players have to choose them this way to get them back)
-goggles (improves sight somehow during scoping, maybe overbrighting player skins)
-engineer kit (clip size +25% for any weapon in hand, also sets weapon jam probability to zero)
Ok, enough random stuff... discuss/add more
