After dotnet/coreclr#27401 is merged, all of the special-cased System.Numerics types will live in S.P.Corelib. This means that the JIT/EE interface method isInSIMDModule can be obsoleted and these types can be recognized via the same IntrinsicAttribute system that other types are using.

After the type forwards get in place on the CoreFX side and that gets picked up by CoreCLR (this is to help ensure the changes can be properly tested), we should update isInSIMDModule to fail when called and we should update all consumers to use alternative functionality.

dotnet/coreclr#27401 (comment) can be seen for more details.