They could still have certain spells be learned as batches, with them being assigned to multiple slots, some kind of selector for which to assign (ie your basic nuke action having a submenu in the Action & Traits where you pick what element it currently is) or a submenu when you actually cast (with potentially the last used element being the default element the next time you cast to minimize steps each cast).

There's a lot of ways they could potentially handle this without completely gutting the range of actions available (ie wiping DoTs out, removing half the buffs and debuffs so everything fits in 15) or removing the elemental affinity/weaknesses system by merging them into generic spells, the moment of truth will be when they reveal the full list of actions. Once they reveal that information we can have more constructive discussions on the topic since right now people are extrapolating based on assumptions that might have nothing to do with what the plans actually are. Of course, all the info being released together would have been a lot more helpful there but between getting nothing until next week and getting this part today with the rest then, I'll take the option they chose.

I would not worry about the animations stuff at this point, of course visuals matter but compared to proper mechanics they really don't stack up in short term importance. Also, they already have multiple visual renditions for the spells, those being maintained (or restored in subsequent patches) and then expanded up is pretty much a given. SE knows visual appeal is one of the few strong points the game had from the start and they didn't highlight the text about upcoming visual upgrades for no reason.