I'm surprised this hasn't been implemented and would love for it to be. Since we all watch on so many services I've begun to use Reelgood some to keep track of TV and movies, shorts, etc that exist in a grey area as to if they are film or television (primarily because of Netflix originals).
My dream would be RT, LB, TMDB (we should all use TMDB instead of IMDB anyway) and Reelgood to all play together. Reelgood is awesome because it allows me to make watchlists and then shows me when they become available on Netflix, Prime, etc.
Anyway, one step closer would be Letterboxd syncing with Trakt.
We love this idea and are formulating some plans around collaboration in general.
This still isn't a thing after 6-7 years?
We have an Export of your watchlist in Settings. If IMDb supports importing it, this should work. Full sync isn’t possible without a free, open API which they don’t have (and neither do we, yet).
What about if we at least enter it into IMDB as watched or add to watchlist it was just auto-sync'd to Letterboxd, or the opposite only? Then I could primarily just use one but it would then update the other.
My reasoning is IMDB's inclusion on TV and Netflix series, I want to have them all in one place but I love the interface of Letterboxd so much more.