Agreed, I have a hard time imagining such a villian coming off as anything other than cartoonish, unless they explain that he's an apprentice of Palpatine and is fighting for vengeance, or something like that. Still, it wouldn't be thematically cohesive with the rest of the saga, which is the biggest thing to keep in mind. They can do both, I think. The rhyming could come in other forms. And it would form a nice alternation, or a circle, between the three trilogies. In the first, the good guys are in power and fighting against a separatist movement, in the second the good guys are ragtag rebels fighting against a dominant empire, and in the third the good guys are newly in power and fighting against a rebellion/invading force of their own.