I also am missing the full-screen button when looking at lyrics in the repertoire. We have a slightly different use, it's for practice!
When we practice, we just use the song list, so we can look at the lyrics (full-screen!) then we quickly jump back and can tweak things if we need to (lyrics, chords, keys, etc.), re-sync all, then try again in full-screen mode.
It use to be SUPER easy, because you had a full-screen document button right in the left-list, the songs. Then you got rid of that and moved it to the right, but at least it was still usable, just took extra time. Now without the full-screen option, it would be a huge pain having to jump into a set list, then back to the songs, make our edit, back to the set list, etc.
I like your suggestion above about using a smart list during a live show (we usually jump to the song list for that too), but during practice this change makes things difficult.
Could you please just add it back in? Thanks! Or at least have an option to allow it to be visible?