I think this will be interesting for online. For tournies folks are generally cool with setting up rules on stage stuff if it affects character viability. Likely if stage hazards impact play too much tournies may just opt for them to be off, but heres hoping that they keep them and just set up gentleman's agreements.
50/50s every round when a pure zoner vs pure rushdown character are fighting, and the game is coin-flipping between the shortest and longest stage in the game. What happens if the rushdown char gets the small map each of the 3 times, or the zoner gets the long map each of the 3 times? That's not fair. Your map choice shouldn't be left to chance unless you click the "random" button and LET IT. But if you are able to control the map selection via external rules placed on people for a tournament setting then you're approaching true balance and not letting a coin flip determine such an important factor.
I think the general tourney consensus would be(as mentioned earlier) 50/50 for first map then losers choice for all following rounds, just like a character choice.
You really don't think people can just agree to a balanced stage between them for the first stage? I mean I know some people will take the 50/50 gamble. But I'd imagine more times than not those people already feel inferior to their opponent or evenly matched and want to take the risk of the 50/50.
I think as MK9 for a example. IF the same system existed. you don't think Cage/Kabal players would likely just agree to a medium sized stage for the first match? The cage/kabal players that take the 50/50 chance are people IMO someone wanting to "take a risk" because they feel their chances of winning are low and they want to try and cheese a win with an advantage match1.
I myself would probably agree to the most default stage for the matchup I'm playing every time for the first match. Unless my opponent wants to take that 50/50 risk.