Since the thread about ARMS being the next big eSport was closed before I clicked Submit on my post, I guess Ill post it here. So think it has some things going against it.
1. A huge barrier is that it's 1v1, not team based, like pretty much every big eSport. In fact the only major ones I can think of that aren't are Starcraft.
2. We don't know what types of modes it has, whether you can spectate, etc
3. It's limited to just the Switch, which shrinks it's potential base
I have no doubt Nintendo will continue releasing content for it. They've shown with Smash they definitely know how to hype up new character releases, so that isn't an issue, and between that, MK8 and Splatoon, they understand the different means of releasing new content to keep a game fresh. However, I think fighting games have a sort of limit when it comes to popularity, that prevents them from reaching the highest peaks of eSport popularity
And I think another major reason is
4. Nintendo still hasn't quite figured out how to capitalize on their big multiplayer titles. At the moment they have Smash, Mario Kart and Splatoon, each which have huge potential to be big, but they've yet to quite figure out how to do so. I think that would be an interesting thread to have (I might make it actually)