It has been 1 year that I requested this on Github, so I am moving the request here to see if more people are interested.
Now that VRChat has decided to add them into the SDK, it has become a real pain to collaborate on these packages. I see more potential with these packages kept as VPM, rather than being integrated within the SDK.
Having them inside the SDK completely destroys their "open source" advantages. Forks, pull requests, and other Git features are useless now.
Keep the open source open. Please remove the UdonSharp and ClientSim integrations from the SDK and let the community collaborate on those like in the past.