Hello, you seem to have a lot of knowledge about how OSM works (Multipolygon). Why then are you creating a note as anonymous instead of fixing it on your own or at least create the note while being logged in? You must have an OSM account, nobody "anonymous" knows about multipolygons. OSM notes are for non-registered website visitors that don't wanna deal with OSM. If you have an account, just fix it.
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regarding your proposal: no, that's not good. OSM community seems to not like relations much if not needed and here it is definitely not needed. They are extremely far away. Refer https://wiki.openstreetmap.org/wiki/Relations_are_not_categories