Built this locally using your instructions and it worked fine for me (despite the singular comment I added). Takes forever to build though, RIP build server.

So I got this updated to SDK 5.0.208/Runtime 5.0.11 locally, mind if I update this diff for that? (Unfortunately 5.0.209/5.0.12 is not available in the source-build repo yet)

Also, I think that once the SDK for 6.0 is available in the source-build repo that would be an excellent time to get this merged as we wouldn't need to worry about packages that only work with 5, only packages that are updated to 6.0 in the first place are eligible for inclusion.

What is all remaining for this? Creating some ypkg macros and a set of policies that .net packages need to follow for inclusion? For the latter I propose that the self-contained feature (where packages copy the parts of the runtime they need into the executable during build time - essentially statically linking the runtime) is explicitly disallowed and packages must be patched if that's the only thing they support.