I asked a very similiar question back in September, and it's covered in the DocC workgroup's meeting notes from September 9th, 2024. (About the "mentioned in" capability, which is currently experimental)
The gist of the flow described in that meeting - a simple pitch to make something non-experimental in the forums, providing the opportunity to refine and gather any feedback about it's operation. Presuming a consensus, then just the relevant PR's to convert the experimental features to default, and updates as needed to the documentation to match the feature's detail.
If it's more contentious, i'm not certain of the process, but based on past experiences, I'd guess that would keep it in experimental phase longer under a clear path forward could be built-up with consensus.
The overlap with what the internal teams may or may not be doing is unfortunate, but I don't expect Apple's team to expose their internal priorities and intended efforts on any sort of granular level. That said, a quick question in a DocC meeting of "Will my effort at .... XYZ ... run afoul of anything being worked on today?"
I found out, for example, that I'd replicated some of David's work with a 6 month delay when I was exploring extracting and rendering documentation from swift argument parser in order to come up with a scheme to document CLI options for swift commands (well, Docc and friends in particular, but it had broader applicability)