On that Angry Birds note, The only way it can happen is if it was one of those out-of-left-field picks that Sakurai likes to add to each title like Ice Climbers, ROB, Piranha Plant etc as a most likely option.
No point of bring up it's Minecraft-like success because unlike Angry Birds, the former actually retained its success long enough for the pick to make sense and didn't fizzle out relatively quickly.
As mentioned before AB doesn't have the relevancy and support from Dedicated Smashers or the causal market nor the Nintendo Connection to make rounds especially compared to Sega's other IP even compares to SMT.
Not every buyout = Smash Pick Potential.
With the resurgence of arcade style Beat em Ups in recent years, I think it would be cool to see at least one represented in Smash. There are a lot of great options to choose from with River City, Double Dragon, Final Fight, Streets of Rage, Battletoads, and more. I feel like all of these games have characters that would fit great in Smash depending on the priorities. My super long shot dream are the TMNT but we’d have to see a big shift in design philosophy for any character originating from outside gaming to make it.
On this front, it would be cool to have a Beat-em up-style mode within Smash itself. Speaking on TMNT, the latest game especially shows that type would fit quite with Smash-style gameplay especially with Smash Run and SSE as being tried going through stages beating up mooks from the franchises selected with dedicated levels and world map.
Has that Adventure-theme going for it whilst sticking to Smash's strengths like WoL. Would make a great addition with all the chaos and madness with Multiplayer or even as a Single-Player style outing.
I still need to pick up Shredder's Revenge