I know, that you spend some time and effort for the implementation of trakt-addon. And as I can see, your where successful.
But I still see some questions here because of different DB-versions for the different kodi-Versiones.
For exactly this situation I am using the WatchedList addon.
http://kodi.wiki/view/Add-on:WatchedLis ... Discussion
It is a very small addon witch does nothing else then synching the watched status of different kodi-DBs. Therefore it is not important. whether you have your kodi-DBs in a SQL-DB on a NAS or directly stored on a device.
In the opposit to trakt it needs no internet connection and is much faster and smarter, very reliable and for the home or local use only.
The addon is very smart - it synchs my watched status in only some seconds directly after starting kodi or spcm or whatever. If you have watched an episode or a movie. it synchs your watched-DB or file directly after it.
So I have exact the same watched status on all devices indepenend from database-version.
Beeing a big fan of MrMC what makes my FireTv to a real mediaplayer, it would be really really nice, if you could implement watchedList in MrMC.
Thanks and regards
SaEt9000