I think that is a great analogy. If you view Bitcoin on the main blockchain as M0 money supply, then side channels like the Lightning Network and other centralized payment processors that have been popping up can be viewed as M1 and more commonly M2.

If Bitcoin's original thesis of truly decentralized P2P cash still holds, then it should be viewed as an M0 money supply. Financial services and products build on top of and separately from the main chain make sense as analogues to reserve banks and payment processors that do not handle the majority of transfers in physical cash.