+1
"And sometimes there seem to be no different RT bits for a bar as I keep pressing the button and keep getting the same bits."

However there is one major difference between EZ and BIAB that I don't believe is resolvable in exact way you described. EZ keys is a pre-determined MIDI phrase based library. You get what you choose. With BIAB it is far more complex as it uses PGM algorithm /randomizer to glue pieces together from existing recorded data. To put this in a real life scenario: Lets say you do partial regen on bar #5 and BIAB gives you 10 choices to pick from. You listen, choose, move on. If you decide to go back to that bar #5 later and try a different stem. What do you think must happen now? Should it give you (remember) same choices in same order or do a new random generation? What is even more complex, if you use a sectional partial regeneration, which could fall on section of 2 bars at once, a freehand selection (not whole bars).

Having said this, this is my take on your wish, that I believe is more realistic to accomplish. Pre-requisite: Non-modal , floating menu - so you have access to refine selection on UI, use main transport controls, etc. (as of now, menu is modal)
1) Make a selection of a bar, several bars, or any segment freehand.
2) Generate unique stems in a list. Click to listen / choose
3) (This is a tricky one) If you like other(s) stems from generated batch - there should be a mechanism to save these "favorite" in a list with location info and ability to insert them in any place of the composition. Since BIAB can save instructions, instead of rendered audio, it should not take a lot of space, but all others, that you don't want must vanish.

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Partial regeneration through the context menu or direct (Ctrl+F8) is one of the most powerful tools BIAB has to offer.
It had been around for few years now. In my view, if to upgrade, it should be upgraded the right way (not necessarily what I proposed), but so it not only does certain new functions, but is fully integrated in new UI / modern workflow.