Ahh ya. Big libraries can have over 30k movies. Emby, jellyfin, and plex can also integrate into Trakt. So it’s already being used in these apps for many users.
At some point though like you say, it's going to become ineffective and you'd probably want to use the "Sampling" mode that is available to only send a random subset of your library to model as a general representation. Though how well this works on massive library remains to be seen.