Is spectator mode even a possibility?

Probably, but imagine how annoying it would be to have a slow online experience, just because some jerk with bad internet is watching you play.

We could perhaps have a central HUB on the Forums where you upload replays, define what type of match it is (1v1/2v2/FFA/etc., What mode [The different Arena modes, Smash, etc.] & What characters are used) and then those could be uploaded to the SSF2 Equivelant of SSB4's Replay Channel where we could connect to it VIA SSF2's Online Menu and view at our leisure
The only problem about that is when Unlockable Characters become a more common thing aside from just Sandbag, there might be a risk of being spoiled by going into the Replay Channel since there will probably be a high chance of Replays of secret folks being posted there once people find out as to how they're unlocked
So that could be a not-good
But Expansion Characters would be neat on the Replay Channel
We could see what characters other people have made at the touch of our fingers, that'd be neat

As far as stages go, my predictions are:

A One Piece Stage: Because I think Luffy will be in the roster. [Thousand Sunny, Punk Hazard, Marineford]

A Sonic Stage: If we get Knuckles or Shadow, this might happen. [Eggman's Lab/ Airship, G.U.N Facility]

A Mega Man Stage: If we get Zero Which I hope happens OMG, then this is possible. [The Final Stage in Megaman Zero 3 with Omega Zero]

a mega man stage and a sonic stage can still be in this game without the characters you mentioned lol

Sonic already has three stages, and Central Highway could easily work as Zero's stage, unless they use his GBA design.

Why not? He'd still be the same character.
, for example, uses his Twilight Princess design, but has stages from Majora's Mask, Link to the Past, Skyward Sword, and Link's Adventure—none of which use a design that's even similar.

My point was that it'd be pretty unlikely for them to include Zero with his X design, since he's a side character. The thing is, there's really only a slim chance his X design could get in. It'd be more likely that they would want the main character of a series, but since Megaman is already in, X would be just the same. If Zero's getting in, its almost definitely gonna be his more recent design.

Where do you get this idea that he would just be a clone, considering almost none of X's weapons in the Megaman X games even work similar to Classic Megaman. Did you even play any of his games?
Just because they share their first name doesn't mean they're the same character.

I never said he would be a clone. Just that they're similar enough in design that it'd be pointless. Imagine if in Smash, you had both Sonic from the main series and Sonic from Sonic Boom. Different characters, potential for a complete new moveset, completely redundant because they're practically the same character.

MY point was that Central Highway would still work as his home stage even if he has his GBA design and only his GBA design.

Then tell me why are Toon Link and Regular Link in the same game.

because sakurai is lazy

Uhh... you know Sakurai isn't the only one that works on Smash, right?

Toon Link is there because of ease of programming. In X's case, as you stated, he would have to have a completely different moveset. X would have no purpose development wise.