We briefly discussed this during 6.0 / C# 10 but ultimately punted it since the ask came in too late. We've had issues where user-written source generators can no longer observe the output of source generated by Razor's:

• Razor Components which are added by a 3rd party source generator do not render if they are added to a razor file using markup syntax. aspnetcore#32253
• Unable to use Blazor components in source generators aspnetcore#32949
• Components added by a source generator work in code, but not in markup aspnetcore#32172

For 6, the solution we gave our users is to turn off the source generator and fall back to our 2-phase compilation process. We'd made some progress discussing this internally, but filing this for C# 11 consideration.