One other issue to bear in mind: it's *simple* to have properties as a
separate thing. I have been following this discussion with some
interest but... well, I don't think I'm particularly stupid, but most
of it is completely above my head.

Saying "here are items, here are a set of properties you can define
relating to them, here's some notes on how to use properties" is going
to get a lot more people able to contribute than if they need to start
understanding theoretical aspects of semantic relationships...