Yeah, its no doubt a long way off, and there's nothing more fanboyish than this kind of speculation, but wandering daydreams as of late have filled my mind with lots of ideas for the sequal to Brawl (no matter how many years down the road it may be).

For One, I've always had the daydream of imagining what the trailer for the new Smash Bros would be like as it introduced the newcomers. I imagine Sepheroth (from Kingdom Hearts) appearing dramatically before the group of regulars surrounded by flames then as he glides down to face them he clashes swords mid air with a mysterious swordman who is none other than Travis Touchdown (from No More Heroes). What a unique pair up. Suda51 worked a bit on Brawl and seems fond of Nintendo to some degree so it wouldn't surprise me if he wanted to see one of his creations put in a Smash Bros. Game.

I often imagines scenes such as the Metal Gear Rex clashing with Fox's Land Master with Rainbow Man (from Rainbow Man) making his debut into the scene. After all Sakurai did say he would like to have Rainbow Man in the next Smash Bros. Perhaps a character from that mech game with the steam powered transforming robots Nintendo put on the DS in Japan could appear to clash with the Metal Gears, who knows.

What of Sora or Cloud (from Kingdom Hearts)? No other game seems to mesh so well with Smash Bros. Atmosphere of whimsical franchise bluring battle. Either would make a great addition to the cast. Imagine Cloud clashing swords with Link or Sora fighting side by side with Pit?

Imagine if you would Samus and Megaman fighting along side against Sigma who had just merged with the Mother Brain Computer. Such a spectacular battle, I could only imagine a Sigma varient of Ridley as a Boss fight. Such wonderous thoughts...

Yet so few candidates really come to mind for new inclusions, and few that could ever trump the surprise of Solid Snake or Sonic as the guests of last game. While I realize they prefer to keep the list to characters who have appeared on Nintendo consoles before I could only imagine the surprise if Master Chief would show up at the very end of the trailer with the sub-text "SMASH BROS EVOLVED". Only a plea from Microsoft could make such a thing happen and I doubt it ever could but what a lark it would be to see something of such audacity occur.

I hope to someday see Super Smash Bros evolve into the Super Robot Wars of Video Game Characters, a grand gathering indeed.

Balance.

Link to original article?

Good online service!

I was actually thinking more along the lines of what characters would you like to see in the next smash bros. Guess I should have said who instead of what.

I wouldn't really call the inclusion of Sonic and Snake in Brawl a surprise, not by any stretch of the imagination... everyone was already practically expecting them to be in there by the time the announcements were made.

As for additions to a new Smash Bros., well, I wouldn't count on too many characters from companies other than Nintendo and 2nd parties. Definitely not the likes of Master Chief. :p And I honestly can't see them adding an endless supply of new characters anyway.
I really can't think of too many improvements I'd personally like to see, apart from improved graphics and improved online. Maybe Tingle as a playable character. ;)

Nude Suit Samus would be a good start.

Edit:

And nude suit Luigi (in order to attract more females to the franchise).

HD graphics

Edit: LOL @ Picachu BTW  XD

Fund it.

What - the usual, more characters, balance, levels, more robust level editor and online that actually works

Who - Little Mac, Isaac (Golden Sun), Crystal (Star Fox), a Magic user from Fire Emblem, Miis

I wouldn't expect many if any additional 3rd party characters. 2 at the most. And for those I'd have to go with Cloud (SE) and Megaman (Capcom) being the most obvious to include. (Cloud appeared in Mario 3 on 3 basketball)