Rowan:
Well, I believe Brion is keen to see 1.5 ready sooner than later - according to http://mail.wikipedia.org/pipermail/wikitech-l/2005-April/028899.html he was hoping it would be in beta a month ago, so landing a change as fundamental as this is unlikely to be popular with him. And for the record, I think he's right - if the unstable branch stays unstable for too long at a time, features that are fully mature take ages to see the light of day.
That makes sense. Depending on when I'm finished, I'll either commit to a separate branch or ask for 1.5 itself to be branched.
That sounds like something a lot of people will like - not so much often-requested, as often-misunderstood-that-it-already-works. One thing occurs to me though - can the "main" namespace have synonyms (or, perhaps, be removed altogether)? This is important because in the Wikibooks scenario (see also something like the Mozilla Wiki, which uses namespaces more-or-less in this idiom), having [[foo]] always point to something completely different to [[:foo]] may not be an ideal way of distinguishing those two pages.
Interesting point. Redirecting pages with no prefix to a namespace might be possible, would that have the result you want? Are there any particular problems that would have to be dealt with in such a scenario?
Of course, as with InterWiki prefixes, the danger is that as soon as someone *removes* such a synonym, all links using it instantly break (or, more confusingly, not instantly, because of caching).
Yes. One major reason to move namespaces into the DB is that we can do proper validations before mucking about with them -- that is almost impossible when it's all done in variables in the configuration files. For example, it's currently completely possible to inadvertently hide InterWiki prefixes or pseudo-namespaces by adding an extra namespace, or to break links by changing one.
One problem that will have to be dealt with is that a change of the language code will require new namespace names to be used. A "Load from language file" link on Special:Namespaces might be a reasonable temporary solution, but in the long run, it would probably be desirable to move site-wide preferences like this into the DB as well, so we can validate changes and trigger certain effects. I recall there was some work on this a while ago, hopefully it can be revived at some point.
Best,
Erik