Topic on Talk:Extension default namespaces

Personally, I think that having site-specific namespaces should be at 100-199. This allows them to show up earlier on "special:allpages" or any other places that lists namespaces by number. Then place all of the extensions.

Or maybe this ...

0-99 - MediaWiki 100-999 - Site stuff 1000+ extensions.

Extensions can reserve a group of 10 (5 namespaces). For most extensions, that should be fine. It is only big ones that have a whole group of extensions that it might make a difference and they need more.

There is Extension_default_namespaces, which manages namespaces for extensions. Custom namespaces should be above 3000. But having some "prioritization" sounds interesting. Maybe you want to file a feature request at https://phabricator.wikimedia.org/maniphest/task/edit/form/102/

While I agree with this in theory, in practice it's about two decades too late to be practical to implement; too many extensions have used (and currently use) the 100-999 namespace number range, and 100-199 in particular has historically been especially heavily trafficked.

An alternative solution to having site-specific namespaces listed before extension namespaces in various dropdowns and the like, would just be for the software to hardcode special handling for the designated range of 3000-4999. With the range's explicit reservation for site-specific namespaces that's not as unlikely of an idea as it might have been in the past, before the current best practices/recommendations were established.