They should just add abilities to the talent trees or spellbook as toggleable unlockables from various expansion content, instead of pruning.
Having them all in our bars at once would be overwhelming, but like, imagine a drop-down selection like PVP talents have, in the spellbook. Prot/Ret Paladins can have Holy Shock *or* Exorcism, for example.
Gimme my spells back dammit