I have 5 B.Net accounts, each with one WoW account.
The same authenticator is associated with each.

I log in, with one password broadcast and then one authenticator code broadcast.

My extra authenticators have arrived.
So I now have 5 authenticators.
Hopefully 1 retains the ability to log all accounts in at once.
I like to get all accounts in fast.

If they move towards 1 code is good for only 1 account.
I will be able to password and authenticator one account.
PiP swap and repeat.
Probably into the game under a minute with five accounts.
Still more of a hassle then the current time/effort.
But that will be better then an imposed 30 second cooldown after each account logs in.