Stalling was banned in SSBB under pretty much exactly the definition Aweshucks gave. You know it when you see it.
Also, contrary to popular belief, it's essentially the real reason walkoff stages are banned in smash. t means people can just stand at the edge of the stage and wait for you to approach, shield grab, and throw you to your death.
Also:
https://en.wikipedia.org/wiki/Running_out_the_clock pay special attention to the basketball section.
So yeah, trying to stop people from stalling is far from unheard of. It may be a "genuine" way of inning, but it's crappy, boring, uninteresting one that is generally not respected and actively rooted out if possible.
Also, once again, esports means we have to think about spectators as well as players. Stalling is beyond boring to watch and will turn spectators away. That's not to say it won't turn players away as well by the way. It will.
It may not be a problem yet, but it's one of the few things I would support preemptive action against. It's better to just not even let people start entertaining the idea than have to have some big debate later down the road with people who only care about winning their matches... in my opinion.