Doubtful. First off, it's unlikely Rebels and Imperials would work together on anything; their end goals are just too different. Second, if you look at other at other sci-fi franchises like Star Trek or Doctor Who, you notice that even with weapons such as the Death Stars, Starkiller Base, or even the really crazy superweapons that Legends provides like Centerpoint Station or the Star Forge, the fact remains that the Star Wars galaxy remains woefully behind its other counterparts when it comes to capable factions. The Star Wars galaxy would crumble if it were to be invaded by some force like the Borg or the Cybermen. Even Abeloth, which is basically the Star Wars equivalent of a Lovecraftian Elder God, probably couldn't go toe to toe against Daleks or Time Lords. Throw in some really powerful entities like Galactus, Cthulhu, or God and the Star Wars galaxy doesn't stand a chance.