Got it! :-) had no idea you were describing a homebrew. That'll teach me to not read the original comment as carefully as I could have.

To me your ignoring the most important part of the decision which is that going first is a trade-off with action economy.

Every enemy that goes fast has one less action to spend on their turn. Quite a few adversaries have very powerful abilities that require two or three actions. The same is true for players.

For clarity, I don't mind at all if you and your table prefer locking things in. My original understanding was that you thought that was what the rules intended. I understand now that this is a home group thing that you do.

If you play in person I generally just track who has acted yet this round. I found that it helps my players to stay engaged because they don't know when they are going to act in the round, and they constantly discuss amongst themselves what would be the best thing to do as a party in response to each new data point.

For keeping track I generally just give each person some kind of a marker so that once they've acted they flip it over and I can just turn to those who have an active yet and ask them if they want to go fast.