Hi all,

I just realised this is no longer required, because it's been implemented via the backdoor.

In v10 the content querying is (read: will be, when released) much more powerful. Category screens actually now also deploy blocks internally to pull out data. You can also do multi-select category reference fields. So you could build in multi-categorisation via template editing, putting in a main_multi_content block that pulls out category entries that match a particular Filtercode query designed to find any entry, anywhere in the catalogue, that might be set to that category.

While this is a bit more complex to set up, it was always a bit of a corner case - the sponsorship here, but ultimately the lack of getting enough, is more of the good efforts of BobS to drum up momentum.

I prefer the backdoor method. It is more flexible in general, it keeps bloat out from the normal workflow for average users, and it removes the need to make really heavy changes across the system that would have made a lot of code far more complex.

I would humbly suggest moving over sponsorship to:
#142 - Merged sitemap API
This is something I'd love to see achieved in v10. We'd be able to simplify a lot of things down, while making things more consistent and more powerful. I may be willing to do it significantly under my own weight, if we can get some sponsorship to cover a non-trivial percentage it.