Jim, the title to the OP "DAW Features In BiaB - Yes/No Why/Why Not" is not the question to me and perhaps others if you think about it from a user experience standpoint.
This post states this is really about UX, found in many creative software platforms. It is not just about DAWs. It is about user friendliness.
So, that answer is obviously Yes.

Having said that, and after reading through this thread I am confused on your dilemma of Linear Tracks vs Charts or Scores with repeats/jumps in them. (invented to save paper BTW)
PGM has already handle that in the Linear track view. They just unfold it all as you can see the bar chorus /repeats in parentheses.

Can they do a better job at it? Yes, IMHO it desires a dedicated "Arranger Track" to cleanly show the parts of the song form. Just as they need a dedicated editable Chord Track in the Track View.

Is there a wall at 255/128 in double time? Yes and no. Think of it as a spreadsheet (in software terms an array). They can play through that 255 cells many times and change the algorithm as they go. They have already solved that by unfolding in the track view.

Is 255 bars still a problem, yes when you consider their double time solution divides it in half to 128 bars, and the solution above only works with entire (their term Choruses), so long songs with different movements are not possible without splitting the song up into parts killing the workflow but I don't this we want to discuss that here.

Studio One (latest version), Win 11 23H2 , i9 -10940X 3.3 GHz, 32GB Mem, a 4K 40" monitor, PreSonus Studio Live III Console as interface/controller. secondarily test on Reaper, Cakewalk, and S1 on Surface Pro 3 Win 10 (latest versions).