This seems to be close to the polymorphism that has been discussed elsewhere, and that seems to me to be a preferable solution. I note that you specifically state
but wouldn’t using relations provide for
I think polymorphism + enhancing relations à la More Capability to edit/view related entities in Collections - aka Subtables is the better way to go.
As an aside, isn’t it the case that ‘embedding views/entities’ is just a way to allow the details of something that can already be #mentioned (view or entity) to become visible at the mentioning level. So you’re basically saving the user having to click-through, right?