the debate format has already been agreed to. I doubt Trump would agree to that.
The format for the first debate was 2 minutes of
uninterrupted speaking for each candidate followed by "open discussion". Trump agreed to that but did not follow those rules or the requests of the moderator (neither did Biden, but to a lesser extent). Unless there was a provision stating that mics must
always be on, then they can change that without changing the overall format. Since the agreed upon rules and the moderator were ignored in the last debate, it's hard to complain too much about changing the rules going forward. Or, if the debate structure really is "no rules, scream as much as you want" then have that thunderdome arrangement agreed upon beforehand instead of pretending to have rules.
Also, cutting the mics can be done perfectly fairly. In the previous debate format they could have had only the one mic on for those first two minutes of each candidate with no problem or any unfairness. That simple. Open discussion relies a lot more on a fair moderator but it would be easy to build a debate structure with strict time limits that would be fair to each candidate and would allow back and forth discussion without the constant cross talk, shouting, and incoherence.
About the only way to keep it fair would be a visible counter showing each candidates "on" time, active and cumulative.
That would be an excellent addition to mic control.