I don't think a rev-lok would work out for trials. When setting up for a big jump, don't you need to rev up the engine then dump the clutch? With a rev lock the clutch would engage after you reach a certain rpm.
The clutch is an essential part of riding a trials bike. Some of the mini-trials bikes have a centrifugal clutch, and it is a real handicap to a kid trying to ride one. You need to be able to use the clutch to regulate your speed, as well as the throttle. There are many trials moves that require the use of the clutch. Even for a novice rider who only does basic turns, you need to have the bike positively engaged when turning or else regulate the clutch yourself. You've got to know and anticipate when the clutch engagement comes in, or else it will throw your body position out of whack.