I’ve been considering moving to Jellyfin for a while, but I’m worried they will do the same thing in future.
Currently would not be possible. Jellyfin does not have the sort of centralized accounts/logins that Plex does e.g. you’re not asking Jellyfin devs for permission to log into your own server. That’s just a Plex thing.
If you’re asking could they add that “feature” in the future? Highly unlikely but I guess anything is possible. Were that to happen most likely the code would get forked into a new project.
PS - Jellyfin itself is a fork from Emby back when those devs decided to close their source. Myself & tons of other people dropped Emby at that point & migrated to Jellyfin. jellyfin.org/docs/general/about/