I expect NST to be working on the next Metroid. They developed Metroid Prime Hunters, so they would be the next best developer for the job besides Retro or EAD.
I thought of this too, and would be fine with it. It also occurred to me that the former sonic designer/naughty dog guy that got hired at NST might be involved. Nobody seems to know what he was hired for or what he might be working on.