Yep, helped a friend install a cruise control many years ago and it had a vacuum servo as the throttle control.
Spent a bit of time researching and the only failures I can find are related to the vacuum servo not working (leaks, diaphram shot, etc.). I found nothing concerning sticking WFO.
With a little engineering, it looks like this could be made to work rather nicely on our bikes.
I also looked around for more information concerning this mod and found these:
