All you had to do was get on the Smash train!
Rockstar Games is one of the most important, successful, acclaimed and influential developers in the history of gaming. It makes sense that they would be in consideration for Smash. GTA alone is probably responsible for ushering the modern age of gaming and many of its changes. Their games are constantly acclaimed and sell tons, with GTAV being the single most profitable entertainment product in history and the fastest selling one too.
Of course, they're a Western company and one of the ones with the least amount of business with Nintendo. They're almost antithetical to each other - Nintendo is a family friendly brand that focuses on gameplay over story, while Rockstar specializes in making adult, boundary-pushing (in themes and technology) titles that tell great stories.
Western devs getting in Smash might be an issue, and Rockstar hasn't had a lot of its defining games on Nintendo systems, but honestly I still think it's a considerable possibility. At the very least, around as likely as Doom. For one, Sakurai values influential titles, and Rockstar's a vaultfull of them. Also, some of their titles have been pretty popular in Japan too (GTA V comes to mind) which is a very big bonus for any Western character.
Now who would rep Rockstar Games? According to the rules that we sort of believe are in place, a character needs to have appeared on a Nintendo platform to get in - at the very least, there are no exceptions to that yet. Grand Theft Auto seems like the obvious franchise to be represented - it's their flagship. The main candidates to consider are Claude from III, Tommy Vercetti from Vice City, CJ from San Andreas, Niko Bellic from IV, Huang Lee from Chinatown Wars and Michael de Santa, Franklin Clinton and Trevor Philips from V. Those are the main titles in the series (except for CTW, more on that later). So let's look at them individually and see pros and cons.
Claude has the fact that GTA III is a landmark title in gaming history that created the open world as we know it. I believe Sakurai would appreciate that. He's also a mute, which might make him fit in better with the Smash crew. Finally, he's got one of the more iconic designs amongst the protagonists (I'd say second to CJ and maybe to the V crew). Also of note is that there's debate among GTA fans on whether this Claude is the same as GTA2's protagonist Claude Speed - if so, then Claude has been on the Game Boy Color.
Tommy Vercetti is one of the most violent GTA protagonists and while a great game, it's stuck between the more revolutionary III and San Andreas so I'd have a hard time seeing him. However Vice City would probably make the best stage.
CJ is the most iconic protagonist in all the series and the star of the seminal San Andreas. He has been cited as one of the nicest and most relatable protagonists in the series. Of all the candidates I think he has the strongest shot.
Niko, like CJ, is also incredibly sympathetic, and his game was the first GTA for the HD generation. The story is somber and sad yet poignant, but I don't really see him being picked.
Huang Lee is the outlier here. Chinatown Wars is not a mainline title, rather it's a top-down game in the vein of the original titles yet taking place in the Liberty City of IV and maintaining the somber tone. The reason I'm mentioning it is that Chinatown Wars is a DS game, and while not exclusive, the game was clearly made for the system and it's the best version of it. Chinatown Wars was acclaimed (it's the best DS game on Metacritic) and I think it has a chance. I guess I should mention that there was also a GTA Advance and so its star Mike is technically in play but it's been largely forgotten.
Finally, we have the GTAV trio. None of them are more important than the others story-wise so all three are in contention. Franklin Clinton I'd say is the least iconic of the three and the one with the most forgettable personality, which could work for or against him. Trevor Philips is 100% the most violent and psychotic protagonist in GTA history and there's no way he would be the one chosen, even if he's the most iconic one of the three. Michael de Santa I think strikes a great balance between the two and I would say is more or less the main character of the game if I had to pick one. All three should be considered simply because of V's massive success, but the fact that there's three of them means they kind of cannibalize each other's chances.
Now who else could rep Rockstar? Well for starters, Red Dead seems to have become their secondary series, so someone from there could work. Red Harlow from Revolver is barely in contention as that game is really divorced from what the series later became and didn't get on Nintendo systems anyways. John Marston from 1 and Arthur Morgan from 2 are both incredibly iconic but of course neither of them have been on Nintendo either. Of the two I think Arthur Morgan would have the upper hand because RDR2 was even better received, but of course 1 could pop up on the Switch any day.
There's also Jimmy Hopkins from Bully. Bully did get on the Wii, Jimmy is more of a traditional hero (he fights against bullies) and he's a kid going around with prank stuff and slingshots so he might be a better fit for Smash. Bully 2 has been rumored for a while and it appears that it might be Rockstar's next game so who knows, maybe we even get the first one on Switch.
I figure I might as well mention Max Payne, who Rockstar now owns. A series big enough to get its own movie, the first Max Payne was ported to GBA, and his slow motion shooting wouldn't be out of place alongside Bayonetta.
Finally, there's L.A. Noire. It's on Switch! Cole Phelps is definitely a cleaner character, if less iconic, and we could have a detective archetype. The downside is that with Team Bondi shutting down, the likelihood of Noire getting a sequel is low unless the recent ports sold really well.
So there you have it, I think that's more or less everyone who could be in. One thing that's clear is that most characters would break the "has to be on Nintendo" rule, but all of the series barring Red Dead have at least one game on Nintendo hardware. Honestly, given Rockstar's pedigree, I can see that rule being broken more than I can see them getting rejected because of it. And of course, given the Switch's reputation as a haven for ports, any of the games from the last two generations could be ported and immediately invalidate any arguments against those characters.
I should also mention that most of their characters fill archetypes not yet represented: the criminal, the cop, the cowboy. And there aren't many characters that can fill those archetypes better. So if Sakurai, like with Incineroar, wants one of those archetypes to play with, we have pretty good candidates here.
As for want, as much as I'm a huge fan of their titles, I can't see any of them being that fun to play as. At the same time, Rockstar has definitely earned its place, and seeing something like "Michael buries the hatchet!" pop up in a Smash trailer would definitely send chills down my spine. So I'll got with the exact 50%.
Chance: 13%
Want: 50%
Specter Knight prediction: 0.44%
Noms: Prince of Persia x10