You are correct is stating that there is no "piece of equipment for MCAS" on the B-737 -8/9 MEL Rev. 1 dated 01/17/2018 (MMEL Ref. fsims.faa.gov) for MCAS, either under ATA 22 or 27. However, MMELs do cover many "distributed" FUNCTIONS. (As you describe alternatively as "migrated".) Even though there is not a single "box" or "piece of equipment", there can be MEL relief if specified, given that applicable (M) & (O) items are complied with. MCAS would likely qualify as distributed FUNCTION.