Seems pretty convoluted and confusing, especially for new / casual fans.
I'll admit, maybe I'm too casual a fan, but during regulation, when there's a line brawl/tons of penalties being dished out, I used to get a little confused as to who's serving and how many men should be on the ice. My current understanding is that coincident minors don't get canceled if it's 5 on 5 that will result in 4 on 4 - but otherwise, they get cancelled. I also think that if there's 3 men on the ice and a third minor gets called, that minor's not served until someone else escapes from the box, because 2 men on the ice is obviously silly. I also get the idea that, in overtime, with one team having 2 minors, it's 5 on 3, then 5 on 4 when one of the guys escapes the box, and then 4 on 3 at the next whistle. But it took me a few months to work that out, since I don't have any "NHL rule wonks" in my immediate circle of friends.
If I'm wrong on any of this, please, disabuse me of my ignorance! I'll confess to occasionally peeking at the NHL rule book online, but sometimes my eyes glaze over. (Sometimes, I'm rewarded by a jaw dropper, like the players-can-be-linesmen-and-refs rule. My curiosity really wants that to happen.)
That said, the 4 on 4 going to 3 on 3 in OT shouldn't cause any confusion....no more confusion than, say, the fact that overtime is 4 on 4 to begin with. One practical matter: I wonder how long the 3 on 3 will ACTUALLY be. Obviously no more than 4 minutes, but in theory, there could be 7 minutes without a whistle. Doubtful, but there could be a chunk taken out of the 3 on 3. I guess that's one of the things to watch for in the AHL laboratory.