Of course I think on the outset one must define threshold braking to clarify the difference to trail braking.
For me trail braking is the classic Skip Barber technique of trailing off the brakes gradually as turn-in begins. This technique allows the driver to brake deeper into a corner and carry braking through the turn-in phase.
Threshold braking (I assume – I don’t use that term… although its a good as any to label the technique) is the use of throttle underneath braking to (1) control rotation more aggressively, and (2) keep the engine revs up at the point of transferring off of braking onto throttle.
Good topic, but I’ll hold off opinion until after we confirm this is what we’re discussing. ;-)