Heh. Well, that one sailed right over my head when I originally posted. :) Thanks.
I guess then, one could scratch that initial idea about starting each comment line with '#@' and instead just take a nod from the way existing POD does it and wrap the texi docs in =pod/=cut blocks.
(Edit: Yes, this wouldn't fix that problem either, though, at least it would look just like plain unadorned Texinfo, so the user would do the usual escaping they do when writing an '@' sign -- which could be pretty frequent if documenting a Perl program. Oh well.)
Anyhow, the whole thing is moot, regardless. It seems that some very smart and experienced people have already volunteered and are interested in putting in the work. Evidently, there's justification for extending Perl 5 POD rather than leaping to some other already-established doc format, and it's accepted that new Perl 6 users will just have to get used to it in addition to whatever other doc formats they currently use for their other documentation needs. Maybe Perl 6 Pod is meant to be general enough to service those general documentation needs as well. Not sure yet.