If we consider changing machtypes, I think that we'd also want to (finally) have different machtypes for tagged integers and raw/naked integers, and change the machtype partial order to make naked integers and tagged integers/ocaml values incomparables.
The additional machtypes would help ensure that we never mistakenly promote or use a naked integer as a tagged integer (particularly as it pertains to GC scanning).
If we consider changing machtypes, I think that we'd also want to (finally) have different machtypes for tagged integers and raw/naked integers, and change the machtype partial order to make naked integers and tagged integers/ocaml values incomparables.