Well, I called it with the stage thing and I feel pretty gratified. I even said before, if the Smash team were strapped, I could see 10 stages being made, but 4? Do you have a bridge to sell me next?
I'll make my predictions on the stages for the new total which would be 5 more.
I don't think that Monster Hunter stage is one of them. It would be an incredibly boring walk-off stage and in order to make it interesting, you'd probably need to fill it up with Monsters from the series. I think Rathalos is the limits of what we're getting from MH. If we did get more than that, like an actual Monster Hunter as a playable character obviously that changes things a bit. Then that stage would probably get an overhaul to be its playable version, I just don't predict it.
I really think one of the stages is a new Donkey Kong stage, and one that is inspired by the DKC entries like Gangplank Galleon or another notable location. I realize that it might be too similar to Pirate Ship from Windwaker's stage but if you look at the DK stages, we have Kongo Jungle, Kongo Falls and Jungle Japes with a few cuts - I can't remember the names of the stages but there was a vertical auto-scroller and then a stage that switched from background-foreground. With such limited scenery and the cuts, and with the inclusion of K. Rool and my personal belief in Dixie, I'd be surprised if DK didn't get a new stage.
I'm going to predict no new Metroid stages - right now we have a nice stage total for the series, it's just hard imagining more - Brinstar, Brinstar Depths, Norfair and Frigate Orpheon. That being said, I wouldn't be ridiculously surprised if they brought back Pyrosphere, just perplexed at this stage in the game unless it's a really neat reworked stage idea.
Actually for the most part, many of the characters have plenty of stage representation as it is, even F-Zero. I am not expecting to have the other Mute City back unlike some others because we have 3 stages already in the total reported. Actually, I agree with
@JDogindy since those kinds of stages like Pokefloats now feel like DLC as stages that the development team couldn't
quite complete on time.
For the other four stages:
2. Golden Sun stage (probably Venus Lighthouse). Isaac is primed and ready to go because he brings something most of the others don't or can't - it's a new series to smash. In modern smash, if you get in the base game, you get a stage too.
3. Alolan Stage. This one I'm hesitant on because Alola was THAT forgettable. I think if any stage is made, maybe they do one that involves fighting in Ultra Space? Seriously, most of the locales on the islands themselves are nothing to write home about which is difficult to do considering it's based on Hawaii. But, I do think we get a Pokemon rep and Alola is basically the last huge Nintendo game that we haven't seen a new stage for (Splatoon, Zelda, Mario).
4. Geno stage. I have never played his games but I'm sure there's some kind of location they can make into a stage. I do think he'll be in this because if they were capable of getting a costume, they can surely get the puppet himself.
5. WTF stage. Imagine if Sakurai keeps the very last stage in the base game from us and he makes this stage into an homage to Smash in general. I don't necessarily think this will happen for real, but I'm very undecided as to what a 5th stage would be. Rhythm Heaven? A stage for Sakurai's retro rep? I'll leave this one in a half blank state.