John,
I didn't know about this:
"BIAB claims to have the intelligence currently to avoid identical RealTrack bits on two tracks from playing at the same time"
I am sure this can be amended and it should be. See below.

"EXCEPT ensure that EVERY bar uses DIFFERENT RealTrack bits"
Here is where things get interesting. Simple answer - bad idea. Hear me out. It will be a bit long.

Since incremental, almost instantaneous partial regeneration arrived, I stopped using initial generation of "what system offered" as final stem(s). Partial regen of individual tracks is a true muscle power of BIAB. It lets you effortlessly to massage the track at almost granular level, to make it fit the best possible way - that this particular track is capable of into your arrangement. If to put in a perspective, think of it as initial generation of a track - a log, and partially regenerated track - Pinocchio.

Likely, many if not most of BIAB folks are either not familiar with this (partial regen method) or tried it last a few years back when it was very clunky. Those who use it are aware that track becomes semi-frozen. Meaning you can still generate any part from any place of the track. However... and this is important as it relates to this thread's request. Just as with non frozen tracks, it is easy to lose a sweet section for good - if you regenerate on top of existing generation. Soo... the true Duplicate track(s) will allow to retain original, while experimenting with a duplicate. Easy way to audition A / B, make changes to any of two (three) tracks- compile.

Yes, I could have made a wish targeting a particular feature, but Duplicate track method is far more universal as it can appeal to a much broader group of people for very different reasons.
For example, FX you mentioned, backup (in the same project), especially useful working with MIDI and others.
And yes, even if some are not familiar they can A/B audition "whole" generation of a track as BIAB initially suggested.

In short, I believe a duplicated track should be identical to "source" track. Until you press "Play", so that users have an option of "freezing" it before it gets regenerated (Play or regenerate buttons) - if it follows what you said on claim of avoiding identical tracks. With my specific main case use, it will not matter, as target track will most likely be semi-frozen anyway.