Smash DLC is about having big game icons join, but I think an implicit understanding with that is that the character must be associated with Nintendo to a degree, or at least "fit" the aesthetic easily in some way. They aren't going to add Arthas or some Dota or League character, for example.
Not saying Nintendo port = Smash Rep, otherwise we'd have Raynor / Kerrigan already (Starcraft 64, baybee!). Those ports / association help make it possible, I agree on that. I'm pretty (overly) bullish on their chances, but I'm fully aware that it's pretty much reliant on Sakurai taking an interest in the genre. Which itself isn't a guarantee.