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.