Replying to myself just to give an update on my previous comment…
This blue post indeed seems to kill even hardware multiboxers, effectively gutting multiboxing as we know it. My take from that post is just plain old alt tabbing and controlling one window at a time is all that they will allow. In any case with the software option gone from the original announcement, multiboxing is dead.
Controlling them “individually”, to me means not even hardware splitting would be allowed, since sending that mouse/keyboard to 2 or more clients violates the blue statement here.