Thinking about interoperability… when I’m running OD&D, something intended for DW is generally of more use to me than something intended for DCC. (I don’t think it’s a coincidence that most of Metzger’s modules are dual-statted for LL and DW.) And Into the Odd reads to me like a set of OD&D house rules (I say that as a compliment).

I do think interoperability is an important common factor, but I don’t think I’d place it in the number one definitional slot.