Thanks for experimenting with this!
I haven't installed it yet - I'm currently running XtreStoLite 3.1.1 with systemless SuperSu 2.74 and a conventional Wanam Xposed arm64 v85 installation on zeroflte (Galaxy S6).
Even with the conventional Xposed installation, toggling off Xposed in the latest rev (5/29) of @DVDandroid's installer and rebooting allows Android Pay to work. ART cache didn't rebuild either as noted in your post.
This is great progress!
Disabling it will not make android pay to work. I just tested it.
I have to use systemless Xposed to pass safety net check.