Hi,
Creating a tight coastline multipolygon relation, such as is done for
Hudson Bay https://www.openstreetmap.org/relation/9441240 and James
Bay https://www.openstreetmap.org/relation/13360255 is at best
controversial and definitely unwieldy.
I hate these beasts with all my heart and thank you for not suggesting
that as a serious solution. Among other things, these relations will
usually require the introduction of more ore less random guesswork lines
that separate them from neighbouring named water areas.
Most people introduce these giant water-area-on-sea relations for the
single purpose of getting nice labels. If we can find a workable
solution that allows people to create labels without having these
polygons, that would be a huge step forward.
Bye
Frederik