Possibly a configurable thing? Just that I've noticed that it doesn't actually ever check to see if anything's changed, which you (currently) have to do yourself by disabling and re-enabling. 30 or 10 seconds seems like a good baseline for a refresh/check rate.

This should be done now

Maybe if the rescan was tied to chunk updates you could scan only the updated chunks to save on performance? You're probably already doing that but I have not checked through the code in quite some time.

You mean for placing and removing blocks?