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I don't think it's really necessary, and of course we want to minimize the workload of our fearless leader. You just can append replies to your original node, just like I did for example with this. If you dig enough in that one, there is a very nice discussion between tilly and tye about our, among others. That discussion started some time after i started the thread.
Clearly TMTOWTDI. It was just such a situation as you describe which inspired my original suggestion. If I had wanted to see discussion about our (as opposed to just reading the docs), I would not have known to look in a thread called SuperSplit, in the Craft section. And indeed, the thread retains that name throughout, so I wouldn't know by checking Newest Nodes that the topic had shifted to our and the like. The idea of the Parlour is that discussions of a generalised but productive nature could be pushed over there (and possibly threaded in some other format, to highlight newness of responses) so as to keep the various departments clear for the purposes 'on the tin', as it were.
Audience? The veteran monks always check new notes in the newest nodes list to browse for replies in threads they like. These ppl will see new leaves on your tree. You always can invite others (who gave some significant input) with /msg to read new updates.
Just as you say - the veteran monks will know. (Although not flawlessly - see above.) Newcomers who may well want most of all to participate in generalised Perl discussion can find the Monastery somewhat daunting, with everything apparently strictly sorted by theme.
XP? Old threads don't gather mucho XP, but I have the feeling you're not such an XP whore. So just reply with an update to your old thread.
You flatter me, brother. :-) But I hadn't personally considered XP an issue. What I'm concerned about is that disucssion of wider relevance can end up buried at the dog end of threads. (Like the abovementioned discussion of our, or the projected implementation details of the Text Adventure Project.) By pulling persistent ideas over to the Parlour, we'd be able to discuss them with more leisure. (The second Text Adventure thread already has a note depth of 14. People aren't going to root around at those bottom ends on the offchance of new relevance.)
Eventually, there comes a time that your modules grow large, and than you need your own mailing list. Consider a sourceforge project in that case.
For one, I've only the vaguest awareness of Sourceforge. For another, the Parlour would be the best place for such ideas _until_ they go critical and need their own managed mailing list.
Just my half-groat in the monastery strong-box.