Not sure there is anything much more than the section you linked.
I can post my thoughts on how I see this.
I think the general idea on what goes there that has kind of caught on with the developers is:
- larger issues that touch multiple repos (example: reduce sum, variadic ode, sparse)
- larger issues that need more detailed explanation thats a bit much for a repo issue (OpenCL kernel generator)
- proposals for changes to the language (ragged, interpolation)
- new algorithms or new interfaces (laplace, cmdstanpy)
I also see it as a good place to hash out ideas, get “consensus” on larger things that will affect anyone (for example: latest Stan CI PR). Discourse topics quickly vanish and it’s then hard to find them even after a week. Much less a month or a year.
Not sure on who can approve, but the way I see it the final approval will always come as approval to specific PRs on separate repositories. This can be used to set up the plan before you dig too deep.