Is there a maximum length or number of tracks for a playlist? I've seen comments referring to playlists of hundreds, even 1000+ tracks, but I haven't found any documentation stating whether or not there is a maximum.
I think the limit of number of playlists is the same as the track limit in one playlist. It is basically a root playlist containing other playlists instead of tracks, so they have similar limitations. But the limit could be set differently.
Max length of playlists related to max number of saved tracks just by the fact they are the same number now. They share similar scaling problems, but they are stored differently, on purpose, so number of saved tracks could eventually be increased, independent of max length of playlists.