Sure they can, its simply a matter or picking what animation is most appropriate (from a ton currently available) and attaching it to the power. Blaze, Fire Blasts highest damage 80ft range instant attack is the same as what Energy Transfer used to be and is currently the same as Freezing touch in the Ice Melee set (among others). I build abilities myself in another private server, its pretty standard stuff.
Bespoke brand new animations would of course be nice but they are certainly not necessary.
You need to get an existing power that has a suitable animation and also has exactly the same animation time as the casting time of the new power as well... that is a lot harder to do than just pick a random animation.
If the animation is shorter than the cast time, you get to move earlier - before it's actually fired off.
If the animation is longer than the cast time, you cant move until x time after the power had fired off.
Also, Just because two animations match cast does not mean you can use a punch to fling fire balls. FX changes may be needed to make the effect come off the right body part.
It really isnt, for every ability thats in those unreleased sets there is at the very least one ability that you can just go to and it will fit just fine, theres several darts.
Animation time is not tied to the animation, its easy to increase/decrease
Fx changes are clearly different and still, theres already a myriad in the game thats easily importable to them.
You are looking for problems that dont exist, in animation, effect and visual terms all the pieces are already in game to make it look great, it just requires someone to assemble (which isnt hard) and THEN, when you have the pieces together, the abilities need balancing. Its pretty much the preserve for one guy on the team and hes pretty busy, but dont make assumptions at where the bottleneck lies, its manpower, nothing else in this cases.