After talking to damentz and heftig, it looks like these patches might be included in linux-zen with the 5.8.6 release.
pre-release linux-zen 5.8.6
I’ve compiled a pre-release and put it here:
https://repo.m2x.dev/current/extra/x86_64/linux-zen-5.8.6.zen0-0-x86_64.pkg.tar.zst
https://repo.m2x.dev/current/extra/x86_64/linux-zen-headers-5.8.6.zen0-0-x86_64.pkg.tar.zst
Gone, 5.8.6.zen1-1 is available
(there’s a corresponding .sig too if you want to validate the packages or install directly using pacman -U)
PKGBUILD: https://gitlab.com/m2x.dev/overlay/linux-zen/-/commit/f86cdf2de706eaea410527122f800bfee95dc9a8
Rebooting to test. 
Edit: Reboot was OK, now to see if it has the same freezes that I saw with -lqx 5.8.5…
Edit 2: So far so good with NFS, let’s try with VirtualBox.
Edit 3: OK, looks good to me. I think this is a keeper.