Like, what if Snoke was an agent of said threat. Sowing the seeds for a wider invasion.
Seriously. It would’ve “subverted expectations” just as much to make the analogue-Emperor a puppet of a greater force. Instead of the total joke we got, he would’ve emphasized the theme of moving beyond the old storyline and its good-bad imagery. He still could’ve been wiped out easily and build towards a greater threat; imagine if the First Order and the resistance had to be forced to work together?
In the future, with more media, it may be possible to heavily edit TLJ and Rise into this film, but that would take an incredible level of storywriting skill.