This may or may not happen, but this would be really nice to have in multigroups.
Actually, CCK for D6 implements different storage methods for fields, depending on several factors. We have per content type table, and per field table. The later is used whenever a field is shared between several content types, or when more than 1 value is allowed for a field, in which case a new column is added to the primary key, the delta.
Well, maybe it is not so complex to tweak the current algorithm to add yet another storage method that assigns a per multigroup table to fields in multigroups.