Yes. This would be very handy for many other things like offline syncing with e.g. Kodi or similar tools. In a mixed environment (e.g. MP2 on the main system, Kodi on TV-Box or Raspberry on other places) this would help keeping watched states in sync without the need to use Trakt on all of those devices...s there still need for the transfer watched states without trakt plugin?
Kodi has a db migration in-build during version changes (e.g. from 17.6 to 18) since ages but still there is an addon for backup and restore of the watched flags available. It's called "WatchedList" and I plan to use this Addon together with your new MP2 plugin to write an automatic syncing tool that uses both plugins to sync the watched states in background...
In the long term I'm dreaming of a "MediaPortal2- Addon" for Kodi to make use of the MP2 Server in Kodi, similar to Plex and Emby... But this has to be written in Python so not too much devs around here can do this, I fear. The chance that this happens is very tiny, but dreaming is allowed... The usage of a full blown Windows PC as HTPC is decreasing more and more. In the long term we need to find a way to make usage of all those tiny, cheap, silent, low power consuming devices that make great HTPC but not running Windows and for that not running MediaPortal. One way would be to port MP2 client to Android, Linux, iOS, MacOS,... something that is not very realistic to achieve. The other way would be to utilize already available stuff like Kodi that is running on every device you can think of. This way would be much less work, I'm sure. But it needs a Kodi Addon written in Python...