That assumes Disney aren't running away as fast as their billions of dollars will take them from the prequels.
It's about my only complaint about the film that the only thing Snoke (terrible name) can be is an evil Yoda.
I'm not sure what you mean by that, and I'm certain someone must have already discussed this theory in this thread, but contrary to your statement I think the only thing Supreme Leader Snoke the Wise (he's so wise!) can be is Darth Plagueis the Wise who mastered life and death through the force, fooled Palpatine into thinking he killed him so that he could get around the rule of two (really, Palpatine, you think such a powerful Sith would just let you kill him in his sleep?), created Anakin from the Force, and has been quietly observing events from the sideline until, of course, his Force project Anakin turned back to the lightside and died. Now Snoke/Plagueis is using Anakin's grandson to take Luke out of the picture and resume his project to some end goal we don't know about yet.
Quite different from an "evil Yoda" if you ask me, and a genius way to tie all three trilogies together. (please don't ruin this, Disney...)
Why should they reference a reviled set of films?
Other than a passing mention to a gungan genocide we all want.
From what we see in ep7 they are not remotely referencing the prequels when every other scene refers to something from the original trilogy.
From a plot point of view there are essentially 3 options.
A/evil dude is actually that big. That's dumb and would not make for a good final duel.
B/evil dude is just roughly human sized. In which case, why go to the trouble (expensive cgi wise) to create a huge sized villain. That massive hologram only makes sense if...
C/evil dude is small. That makes for a more shocking reveal.
Plus it refers and counterbalances the original trilogies Yoda figure as the good guy.
I'm not saying evil dude is literally of yodas species, but it only really makes sense for him to be small.
Why would there need to be a final duel? I don't remember Luke dueling with Palpatine. Also I don't see why he would be an "evil Yoda" if the only thing he has in common with Yoda is the fact that he's small, if that's all you got out of Yoda then I think you missed the point.