Without support for include/join, I don't see the point of migrating my existing .NET code (using the existing MongoDB LINQ driver, which provides richer capabilities) to use EF Core. Relationship/navigation support (enabling to query and update multiple MongoDB collections) would be the game changer here.

I've tried the preview, but found that anything except simplistic demo cases doesn't work. There's still a long way to go (as open issues reflect), pretty surprising this was announced as GA recently.