I think one of the reasons not to use @system is that if anyone flags the post (eg. a ‘something else’ flag to inform you of a typo or error, etc) then those flags don’t currently appear in the review queue and quietly disappear into the void. 
[1]
The @Discourse user is the main one for meta docs. It originally began in a similar way to what you say, as having ‘official’/current docs faced by an inactive member wasn’t ideal (and it also cuts down on quote and link notifications for active members who owned the popular ones that are widely shared).
I think as long as the people responsible for updating the guide have it set to Watching to keep an eye out for any feedback (or at least check in regularly) then it can work quite well.
though the ‘something else’ flags do generate a PM to moderators, so maybe those don’t get quite as lost as off-topic, etc
It may depend on whether anyone has changed the notification level of the moderators inbox ↩︎