I don't think a walkway between Z and B-Non Schengen is in the current plans, and neither is bi-level gates in B (except for the one they sorta kinda have).
A minimalist approach would just mostly leave the B arms as is, but change up some of the clean/unclean areas.
E.g. the walkway from non-Schengen B to the SkyTrain is currently unclean, you rework things so that creates a clean path.
I have no idea how ambitious they are going to be...