I don't think the shock beam should be nerfed too much. The whole point of the shock rifle is supposed to be it's versatility, not just the raw power of shock combos. One of the many versatile features of the shock rifle has always been, and should continue to be, it's ability to attack competantly at long range without having to have a sniper rifle. While it should not be equal to the sniper/lightning at long range, is should be able to hold its own.
I think the most apropriate aproach to the shock rifle is to keep the stun/knockback the same but reduce the damage. Emphasize stunning the opponent and pushing off ledges over killing him outright, because that's more unique.
I think the ROF should also stay relatively fast, because the sniper rifle and lightning gun have allready been relegated to slow ROF railgun-type weapons. That way the shock rifle stays more unique and offers a faster rof for hitscan weapons. If the damage is low enough, the fast rate shouldn't be a problem.
I also have to disagree with the idea of "ghost shock cores" that don't interact with players at all except to activate combos. The shock ball has always been open to players as a means of close range defense. It's like an akward cross between a rocket, a pulse/link bolt, and a flak blast. Also, the simple fact is not every UT player is a combo god, and players shouldn't have to be a tourney goer just to do damage with alt fire. Just reduce the ROF or the damage, or something. IMO, combos should not be the sole purpose of the shock rifle or even of the alt fire.
As for the combos themselves, in hindsight, it's a little surprising that they've always been given so much power. The simple ability to detonate them on command rather than on impact with an obstacle would make them usefull and powerfull enough on their own. The fact that they also deal crippling damage is beside the point. I think the combo's tactical advantages should be emphasized over it's raw power. The main advantage of combos over a simple alt or primary fire should be the arbitrary, mid-air detonation point and relatively large blast radius, not the raw power of being one of the only sure methods of a one-hit kill in the game. If the target is not in a position where a large blast radius or set detonation point is required, than a regular shock core or beam should serve just as well.
And again, I have to emphasize, combos should not be the one and only purpose of shock rifles. Their main point is that versatily; moderate long range ability, moderate close range ability, and the combo fire for special situations.
As for ONS and vehicular combat, it sounds like the main problem is that other weapons aren't effective enough against vehicles, not that the shock is too effective. To an extent, I think vehicles bring things into a completely different ball-park, so adding weapons like the AVRIL built to deal exculsively with vehicles make sense, because they allow you to give footsoldiers a chance without messing with an balance that is allready delicate as it is in man vs man combat. However, the fact remains that the game is built around all these weapons, and leaving the AVRIL and shock as the only usefull weapons and ditching all the others is a cop-out. The weapons and vehicles need to be balanced so each and every weapon is as usefull in vehicular combat as with anti-personell combat. THe AVRIL is kind of a deus-ex-machina gimmick aproach, and for all I care, it could be tossed out in favor of making the other weapons more vehicle effective.
The same applies to range. Granted, the average ranges of UT's weapons is pretty well maximized compaired to games like Halo, where lots of spread is added to every weapon for no good reason and almost everything is useless beyond 20 yards. But it's still pretty low for the projectile weapons. I think the primary answer is acceleration. The projectiles should speed up drastically as they travel over long distances, instead of remaining the same all the time. Rockets did this in UT99, which is why they always seemed slow when firing at nearby enemies, but seemed to FLASH past you when fired at you by someone on the other side of Face. Acceleration was removed in UT2003/4, but if it was added to all projectiles in the next UT, they could maintain their effective range better over wide varieties of distances.
Also, for weapons like the minigun and assault rifle, using higher damage values coupled with larger spread will offer about the same level of power against small human targets, but will increase effectiveness against large vehicles targets.
The other thing is they could just make seperate versions of the weapons for ONS with increased power, speed, and blast radii, or whatever changes are necessary to balance things against vehicles, but since the modifications would be ONS-only, they would not interfere with DM, TDM, or CTF.