I’d never thought about it clearly, so thanks for this model.
A behavior I’ve observed (and participated in) that you don’t mention: the group can temporarily splinter.
Picture 6 people.
Someone explores topic A. Two other people like the new topic. The other 3 listen politely for 1-2 minutes.
One of the three bored people explores topic B, addressing a bored neighbor (identified by their silence). The third bored person latches on to them.
Then both conversations evolve until one dies down or a leader forcibly merges the two.
(By forcibly merge, I mean: while participating in conversation A, listen to conversation B, wait for a simultaneous pause in both, then respond conspicuously to conversation B, dragging most conversation A participants with you. I have observed myself doing this.)
(Single participants can also switch freely.)
(I have observed this to work with close friends and relative strangers, but obviously strangers need leaders/confident people to start new conversations, because they have to be in explore mode.)
I think this lowers the exploration barrier, compared to your model.