Many thanks for the updated textareaId documentation - that's very helpful. I've incorporated it into the Readme.md for the upcoming release.
For now I've also added the sync_interval_secs UI parameter to the other two UIs that don't automatically keep the textarea in sync: gapfiller UI and table UI. However since the overheads with those are likely to be always small, I might just use fixed time intervals for them. It's easy to add back in again if needed in the future.
Since syncing the UI contents back to the textarea doesn't in turn sync back to the server, there's still an element of risk with relying on quiz time outs for submissions. If, say, a student's laptop battery fails, or the network goes down, all a student's work could be lost. So I prefer to always provide students with at least a precheck button that provides some level of sanity check to the student while also submitting their work to the server.
If you're interested in checking out the intended new version, you could pull the Development branch from github. It's still in pre-release state, but I think it's close to release and I'm about to install it on our production server for this coming academic year. However, the Readme documentation and some of the inline documentation hasn't yet been updated and of course there are still likely to be a few bugs. But I'd certainly be grateful for any feedback.