Long comment warning
I think the thing i want the most from MP4, storywise, is that sylux will be something to remember by. I want him to be remembered as a great antagonist/villain/whatever he is, not just by metroid standards (because there are no such standards lol). I truly hope he is not a two dimensional character and more: that his developments, personality and whatever wont be boggled down in scans, that would be terrible.
Second: I find corruption's cinematic traits to be quite impressive for nintendo's standards: to this day it still features superior VA than the latest Zelda games, its animation and cinematics were surprisingly well made despite being few and short (such as rundas freezing up the space pirates right before his battle, how the camera doesnt cuts and is very dynamic), the setpieces, despite being relegated mostly to the beginning, are all very very sweet and all. But i dont think of corruption as the standard MP4 should follow. I think it is quite unpersonal and more than often, shallow. I hope, i truly hope MP4 is y know... not about space battles and the like, i would like a story set on just one planet and deal with small scale stuff, i find that more impactful.
Third: I hope retro gives more focus on visuals than words. Scans are nice, but i truly hope they do some heavy focus on what you re seeing than what is written. That does not mean i dont want scans, just that the most interesting stories are the ones that are happening, not the ones that have happened. That ties in what i said about Sylux above, and adding to it, i dont want him to just be everpresent through the game, but to be something players want and are interested in to know and to battle and to see.
Fourth: More setpieces pls and scripted events pls. Loved those in corruption. I would like if MP4 was less linear than the trilogy, but i dont want it to be botw in space, so i think this would be a very decent way of telling stories without overuse of scans.