I don't think there's anything to say that hasn't been said on the
forums already.

I'm just a user, but I argue that just because the Chaotic-AUR
maintainers want to avoid epochs at all cost doesn't mean it's the
right thing to do. Yes, they should be used sparingly, I agree with
that. But I feel that the end-user experience is more important than
wanting a "clean" version number.

given the answers that were given so far, and given that there is no
authorative answer since 6 days, can I conclude that there is no
authorative rule regarding the use of `$epoch` as questioned (only
suggestions, but nothing that must be followed for an AUR package)?,
and I can mentally "close" this issue?

Some answers in the forum were already given, the wiki itself for PKGBUILD [1] states:

> Used to force the package to be seen as newer than any previous version with a lower epoch.

This is clear for anyone, its use covers exactly the cases where the upstream version numbering changes or when the downstream version number change would make the newer package with a version number previous than the previous. For git packages the pkgver is set by downstream in the PKGBUILD so it applies also to the previous condition.

There's not any exception for VCS packages (including -git of course), so there's no reason for not applying the change (setting the epoch) when the version numbering change, regardless being a VCS package or not.

Regards

[1] https://wiki.archlinux.org/title/PKGBUILD#epoch

-- 
Fabio Castelli aka Muflone