It seems there are two prominent forks. The one available from popcorn-time.se seems to be developed in private and might ship with adware. The one available from popcorntime.io seems to be developed in public.
Both seem to use yts.to, as a movie directory. It currently has 4088 entries, which is not a large number (Netflix: 7125), but seems to be very heavily weighted toward recent U.S. mass market movies. Doubtless there are pirate communities that cater to older, non-English, and art releases, but YTS and by extension Popcorn Time definitely does not. Unfortunately this only reinforces my impression that piracy provides price discrimination, customer retention and marketing services, gratis to Hollywood.
I looked for a libre or public domain movie to try watching in the Popcorn Time application. I found only a few old films in the catalog that may be in the public domain, at least in the U.S. I tried the oldest in the catalog, Way Down East (1920; Wikipedia, Commons).
It took 7 minutes to start playing the movie. That’s impressive, relative to waiting for the entire file to download, and that the bandwidth is presumably all coming from distributed peers. But it’s not at all impressive relative to near instant start on streaming sites. Seeking seemed to not work, but perhaps would’ve had I downloaded the entire movie. It’s possible that more popular titles would start playing faster. I admit that watching a few minutes of an unpopular title and trying to seek is a totally unfair evaluation!
I suspect that web streaming, even if assisted by bittorrent, is a better primary distribution mechanism for premium libre movies. Downloading a dedicated application and waiting minutes to start watching are each high barriers.
But a centralized premium and libre video community might also be better able to coordinate to get distribution of premium and libre video in channels such as YTS and Popcorn Time, and that would be worth doing.