Before you get carried away, remember that power-sets =/= animations. Your rifle can shoot ice or acid, or cute fuzzy puppies, provided the power-set is available. Alternatively, you can shoot bullets out of your eyes, if you're into that kind of thing. Power-sets are the effects you that lay out to either help or harm the target, and in CoT, they're independent of how you deliver them.
But, lets get to the issue at hand, shall we? When including a desired powerset, remember to consider what kind of theme of effects you'd like to achieve, and how they would, at least theoretically, balance against the other sets. I will go ahead and list out the practical default we've come to expect:
Fire: Fire/thermal damage, Extra DoT, but limited control/debuff compared to other sets. Weak single target DPS, but strong Area of Effect DPS
Ice: Cold/thermal damage, More control/debuff focused with cooldown reduction, freezing, etc. Not sure where the Single-target/AoE balance should be on this one. I tend to think it should be more single-target.
Energy: Energy or mixed (energy and physical) damage, control via knockdown/back. Strong single target DPS, but limited AoE DPS.
Firearms/ordinance: Mostly physical damage, balanced mix of single target and AoE, and mid-level of control/debuff
Psychic: Weak theoretical DPS, but bypasses many defenses.
These are the ones we all pretty much know we're going to get, though my views on how they will be implemented balance and theme-wise is naturally only my own wild donkey guess.
Any other ideas?
Sic Semper Tyrannis