There are about 5 differnt sources I say can attempt a Smash-eque game. they are...
1. SEGA. They have possibly the most IPs of any Company, Conssting of ongoing seriies such as Sonic, Valkyria Chronicles, and Virtua Fighter to Clasics like Comix Zone, Alex Kidd and Vectorman. On top of that, thy already have an established spinoff series with Sonic & Sega All-Stars, so sliding in a mascot fighter under that label would be easy. Also SEGA could go take even more surprise risks with thier roster then Nintendo even does, as shown by having the Outrun car be an actual fighter in Fighters Megamix. Only bummer is they no longer have Platinum games, so Jack and Bayoneta are out....but with so manoy other IPs they have more then plenty to choose from.
2.Namco. These guys not only have the skills o do one due to being developers of the new Smash, but also for birthing the genre that Smash stemmed from altogether with The Outfoxies. Besides the obvious PAC-MAN, they also have Tekken, Soul Calibur, Klonoa, Xenosaga, .hack, Tower of Drauga, Dig Dug, Mr. Driller and for too many arcade games to draw from. and it wouldn't really be the first time, as PAC-MAN Fever crossed over some characters in a so-so Party game.
3.Capcom. kind of an ovbious, but at the same time not exactly. See, they already have an arena fighter with the well loved Powerstone series, as well as crossovers with the _Vs._ and _X_ series. owever, due to the resurgance of crossover fighters, and the loss of the Marvel Liscense, combined wih their decades of experience with Fighting Games, it may be more of a case of not If but When. and speaking of Marvel.......
4.Disney. this is one of those choices that sounds odd at first, but makes perfect sense in thought. with an 80+ year legacy in film and television, Disney would be an absolute monster if they made a smash-like game. besides the obvious Mickey and pals(preferably the awesome 2013 incarnation that brings back the classic delinquint Mickey vs. the Mr. nice guy version of him from the 80s-90s), They can also draw from all their films, going from the first ones Snow White and Pinocchio, the best ones like the Lion King and Beauty and the Beast,TV shows like Gargoyles and Gravity Falls, Modern Hits like Frozen and Wreck-It Ralph, and Cult Classics like Tron and The Adventurers. but now is where is when things get crazy-when you apply all the things they own to the mix. with Touchstone, we get things like Jack Skellington and Roger Rabbit up for play.Oswald(Walt's original creation) was bought by them from Universal in 2011, allowing fans to play out the sibling battle between him and Mickey. Pixar's works pretty mucgh need no intro, as Buz/Woody and Mr. Incredible can speak for themselves. and last anc certainly not least, Marvel and Star Wars....nuff said.
5.Cartoon Network(again.) I feel these guys deserve a second go. Punch Time Explosion was admirble, but was ultimately hampered by what was clearly a low budget(like PS All-Stars was.) Kudos to those who tried making a scene for the game, but it was sacked from the get-go.with a better budget and more support, CN can become a real hit, as they were on the right path of getting the Smash formla right. and also, MAKE SURE TO GET MORE SERIES IN THE GAME. It was almost shocking exactly what series wereomitted from the first game-Courage the Coawardly Dog, Ed,Edd n'Eddy, Evil Con Carne and Adventure Time had no representation at all to the shock of many. Make sure to get those, as well as more obscure classics such as I Am Weasel and Robot Jones. Modern hits such as the aformentioned Adventure Time, Gumball, and Regular show are definates.And while you said last time Adult Swim franchises are out of your control, you DO own Space Ghost(as he was the narrator of the last game) so him, Brak, and maybe even Birdman would be cool too. and to top the Captain Planet reveal, I say Hanna Barbera reps would work-Flintstones, Jetsons, Scooby Doo, the works.