I'm kinda thinking the same. I'm hopeful for Metroid to be ready to wow us next year, but when they couldn't even give a little bit of visual this year... odds don't look great.I don't see Metroid Prime making next E3 in a playable state. If they're just now starting development it's likely a 2019 title.
Beyond that, Metroid Prime is gonna have to do something really groundbreaking to live up to the hype that Breath of the Wild and Mario Odyssey generated.
I can see it being really impressive when it does show up though. Zelda and Mario both had a certain level of predictability; a new game like Mario 64, a more open-world than usual Zelda. But both knocked it out of the park and really over delivered on those concepts, while also adding surprises we didn't know we wanted.