Racecar Engineering article about it.
Lovely animations about how it works.
This is NOT preseletion as used in the 30's using a billion clutches and epicyclic (I even had to read up on this just now as its so antiquated i'd never heard of it). This is the most likely current method of F1 seamless shift.
I have studied the zeroshift system in depth. I suggest you look carefully at it again and be certain of what you define as 'engaged'.
The Wilson gearbox uses a number of brake bands.
One band for each gear. The bands grip a drum, which is part of an epicyclic gear set. One band begins to disengage as another begins to engage, the time between one gear being engaged and driving and the next is a direct result of the slip between the band friction material and the drums. This 'wilsonshift' time is at least as good as the 'zeroshift' time comparing the delay between one gear transfering torque and the next. True, the Wilson is very heavy, old fashioned in every way but it is STILL as fast on shift overlap as any modern gearbox.