BTS usertag and X-Debbugs-CC for x32?

Greetings.

As some of you may know (or have noticed), I've been in the practice of
reporting bugs against packages that recently emerged from NEW and
proceeded to FTBFS on some or all architectures.  Every so often, I
encounter a bug specific to the non-release x32 architecture, which runs
on amd64 hardware and does not have a dedicated lists.debian.org list.

When reporting x32-specific bugs (most recently, qbs bug #884472), I've
been specifying a usertag of x32 with a user address of
[email protected].  However, per a recent off-list
discussion with pabs about standardizing architecture usertags in
general, I see that the wiki page[1] now says the convention has been to
use [email protected] even though that's not actually a list.

Should we stick with that convention or switch to a different address?
Either way, pabs has a script that can adjust any necessary metadata.
Also, Adrian G. recommends explicitly copying porters on these bug
reports, generally via the usertag's associated user address.  What
porter address(es) should we use here?

[1] https://wiki.debian.org/Teams/Debbugs/ArchitectureTags