Interesting. I can see that being handy in periodic scripts, but it would need to be more than what threshold recording is currently using. Threshold record works by looking at the sample levels in each audio block, but there is no "memory" of that. On the next block every sample could be zero so unless the script caught it at exactly the right time it would never see it. For periodic scripts, it would need to be more of an average level with a decay so you have time to see that it happened every 1/10th second. An event script that fires the instant the threshold is reached wouldn't have the observation window problem, but without some kind of limiter on it, it would just be running all the time as you play above the threshold. Definitely something we should have, just not sure about the best way to do it.
This sounds related to your other post about scripts that trigger on a drum beat to auto-select the track. I'll get to that one in a minute.