IMO A major reason to update to 64 bit is to support 64 bit VSTS. All my VSTs are now 64 bit and I just don't have days to spare to double install them all so I can use them in BIAB.
Its true that there are still 32 bit VSTs. In Cubase you can use Jbridge to 'wrap' these for 64 bit. I could not say this would work in a new BIAB 64 bit though. Depends on the quality of the rewrite.

There are so many reasons for a total rewrite of the program code, (inc a new sound engine Joden)I won't list them all that would be tiresome.

So, think it out. IF you were going to embark on a rewrite then would you do this in 64 bit or (only) 32 bit, or both.
I think that if you were to write it would be at least in 64 bit and hopefully in both, but surely not ONLY in 32 bit.

I am not sure if you can compile 64 bit code in 32 bit? It may be a semi-automatic process? Not sure...

Zero

Win 11 64, Asus Rog Strix z390 mobo, 64 gig RAM, 8700k