just make a classic+, separate from museum classic, that has retail models by default, guild banks, karazhan crypts as a dungeon, emerald dream as a raid, medivh’s tower as a dungeon, high elves for alliance, ogres for horde, 4th spec for classes, and various/sundry experimental things they wanted to do but never got around to it, for whatever reason.
maybe we could get a whole season regarding the repair of gnomeregan city and let the gnomes get their home back
4th specs could be used to bring race requests in that have been thus far denied because of how hard it is to create armor for them. examples are dryads, keepers of the glade, ethereals, liches, banshees and so on.
the 4th spec would have a form talent in its talent tree that could be specced into and provide specific perks, such as dryad/keeper of the glade form for druids, would be some buff to fae magic and the 4th spec itself would feature fae spells.
warlocks could get a necro spec as their 4th spec, where the specialize in undead pets like val’kyr instead of demons and have a liche or banshee form talent.
shaman could get a bard spec as their 4th spec, where their totems are replaced by troll tribal war drums, each provided some group wide buff. they would place them directly on the ground around them in a semi circle and run back and forth between them to provide some group effect. interactive totems.
for example. 
mages could get a wizard spec as their 4th spec. see the floating dr. strange mog on the left *play video to see it (warning language),
that could be the wizard form, always doing the floating crossed legged monk thing, but the wizard spec itself would be all about controlling time.