Just to be sure, "Set All To" does not influence hidden players at all, right? Of course it should not; I didn't test.
Nice addition the Default, but it is going to be redundant for over 90% of the games, having all default to Human, and this is how TripleA games are supposed normally to work.
I suggest when all the players in the game, but the hidden ones, are of a same Type, then that type is not availabe in "Set All To", but you have "Default (Type)".
For example, in over 90% maps you would not see "Default" and "Human" (doing the same), but a single "Default (Human)" choice.
Not a big deal, but I just don't like to see multiple options doing the same thing, especially when this is going to be the standard.