i personally would think darth plagueis would be more related to the story then anything
imagine if starkiller had a sort of vision about darth plaueis with plagueis revealing all of the emperors secretes and weaknesses ( as far fetched as that sounds)
Would be cool to fight him and maybe gain his respect.
And yer as for reven, i dont think he would really have any relevence in the story lol
as much as i also love him.