I started typing this last night. Fell asleep, went to work today, continuing on!
Metroid currently has 3 main gameplay types: Platformer (Super Metroid), First person (Prime), and 3rd person (Other M).
I think Other M's gameplay was fantastic, aside from the very few times you were forced to scan something in order to continue the game. I don't, however, think it should be used as the gameplay for the Wii U title (I think it'd be great for the 3DS, though). Someone, I think in this thread but I haven't checked, said here that they didn't much like the Prime games because they weren't fast enough, and I can agree when you compare Samus's run speed between Prime and Super Metroid, or between Prime and Other M, even.
For example, playing Prime with the run speed of Super Metroid would prove incredibly difficult with screw attack (changing directions is a strange problem, which is why it was reduced to "gap crossing mechanic" in the Prime games; Other M did it better, but made several rooms pretty goofy and easily skippable) or incredibly bland with the speed boost that activates after running in a straight line for however long (I like that Other M used this instead of some form of fast-travel, but there are slightly fewer places to use it than what might make it more useful - I found myself frustrated going through some areas of some sectors that just weren't long enough to activate the speed boost, even though it's more "engaging" to shoot baddies than run straight... anyway, I digress). Likewise, playing Super Metroid or Other M with the run speed of Prime would be mind-numbingly boring, which is why that speed works only for Prime, and it's a good speed for itself.
Nevertheless, I don't at all mind what style the next Metroid game uses.
As for story, I'm slightly torn with my one idea. I really want the whole of Other M to continue to be discardable from the canon because of how excruciatingly bad it's left off the series, but I really think that Samus's time as a GF soldier, something admitted early in Other M, might be something fun to explore. For that chunk of story, I want something similar to the final act of Prime 3, where the GF soldiers are with you and sieging the Pirate Homeworld, right?, but maybe Samus isn't meant to be in a platoon/squadron, so Adam splits up the group like he does in Other M to investigate wherever it is they are, and then they get back together and siege the place, I guess after enough Space Pirate intel has been gathered. But this means taking more orders from Adam, and I don't like that at all... But I'm not a video game writing team and I can't figure this out by my lonesome. Maybe there's a way to make it work.
Or perhaps, we see a game that perfectly bridges a gap between two games; Maybe we can have a game that finalizes the timeline of Samus's life - we know the string of Prime games and then the relation between 2, Super, and Other M, but which series of events happened first is still up for debate (unless I missed some things, please say something if I did). On the topic of 2, maybe we can have an official Return Of Samus remake (and the name would be COMPLETELY fitting (Other M was not Samus in some people's eyes)) or even an extension - but while Zero Mission extends the original NES Metroid at the end, this could extend at the beginning (since extending the end would bleed directly into Super Metroid), with events leading up to and stating the reasons more explicitly as to why the extermination of the Metroid population of SR-388 was necessary for the GF.
OR MAYBE we pull off Metroid: Ocarina of Time, and open up separate timelines for future games to travel down for the next 20 years. This could be a way to explain Ridley's repeat appearances less repetitively than "they reanimated him again," which, to me, is completely fine for as many times as it's happened yet, but I think just one more time might make it stale, especially to people that think it's already stale.
