This really seems odd to me. Taunting is actually a part of some of the cast's move-set. Kirby really comes to mind, but there are others, and why even limit people in such a conservative way? Smash 4 did a good job of rooting out taunt parties with the taunt limit, and now we have even stricter rules to snuff taunt parties (the idle thing).
It just feels off; taunts are a fun feature, and guess what? People are going to find new ways to do it anyway by just teabagging people instead. Is that what Nintendo wants? Forgo taunts which are unique and actually took work in favour of a player mashing down on the stick instead? Lol
EDIT: Tested: Kirby CANNOT taunt online either.