One, so that it's already ready if I ever need to use it seriously, and two, so I can continue to observe its progress and dependencies.

I suspect Plex will not give us a lot of warning if they decide that old lifetime passes aren't good enough anymore. Money grabs like that are best as a surprise.

I have two Plex servers I maintain, for myself, friends, and family. Both also have jellyfin serving the same sources. It's trivial to maintain them side by side. Since it's there, I can easily use it occasionally and see if the things I don't like about jellyfin have been fixed.