OK, apparently the time is still not so 'right' yet, so let me looking at it a little more.
The word MDIL is not a new thing, we have seen it in Bartok before:
/TargetMdil=<bool> (currently False) Target MDIL rather than native code
/TargetMdilEHPerBB=<bool> (currently False) When targeting MDIL, emit separate EH records for each basic block
/TargetMdilBartokRuntime=<bool> (currently False) When targeting MDIL, assume that libraries include the Bartok runtime
/ClrMdil=<bool> (currently False) Target/consume CLR-MDIL rather than Bartok-MDIL (not complete)
/RedhawkMdil=<bool> (currently False) Target Redhawk-MDIL rather than Bartok-MDIL (currently implies ClrMdil as well)
/RedhawkBaseClassLibrary=<bool> (currently False) Generate MDIL for a Redhawk base class library (include well-known types table in the CTL)
/MdilV2=<bool> (currently False) Use version 2 of the MDIL instruction encoding (automatic/required for x64)
So there were CLR-MDIL, Bartok-MDIL and Redhawk-MDIL, and also MDIL v2, and thats many years ago.