I'm happy you're so confident.
Well so far we have 4 potential newcomer characters hinted at with stages (Chrom with that Fire Emblem stage, Little Mac with the Super Punch-Out!! ring, Miis with the Wuhu Island area on the Pilotwings stage, and Ridley in this infamous bastardized scene from Other M).
I think Sakurai is trying to troll us, and I expect him to do this with a Donkey Kong Country stage as well (teasing K. Rool). He knows that those 4 characters plus K. Rool are the most wanted Nintendo-owned newcomers.
We all know Little Mac is gonna happen, and we're pretty sure K. Rool and Ridley are gonna happen (don't read into that quote; remember Ness "who was in smash bros up until now" guys). Miis aren't too far behind those two, and eh, Chrom's "chances" are kind of up in the air, but still very reasonable.
I also think Sakurai has never played Metroid before, and I think his stage choices per game continue to get worse and worse. Seriously, can we pulled the starting pitcher and go to the bullpen already with stage selections=??? Or you know, actually make a stage from actual Metroid fans=??? Or you know, get a actual DONKEY KONG COUNTRY stage in Brawl instead of 2 stages that are rarely played by anyone=??? Oh, and I bet the layout will be crap like Norfair again, or it will have too much lava interference to where the stage dictates way too much.
Also visually, Skytown Elysia on Metroid Prime 3 looks far superior than this stage, and that was on that hunk of outdated crap we call the Wii. That says a lot about how bland this stage is. This stage looks blander than the first God of War game. All this stage has is the lava bright colors and lots of dark, gray, and boring.