You have to pick the right tool for the job. Calibre is not and will never be some jack of all trades collection mgmt application. It is for managing book collections, no more, no less. Yes there is the odd user who "bodges" in some of their other data in there, but they do so knowing it will always be constrained by terminology and limitations that make fundamental sense for books and not for anything else.
Any application out there that tries to be some sort of general collection app becomes a jack of all trades, master of none. How could any general collection application compete with the likes of Adobe for photo mgmt for instance? Or any of the squillions of recipe applications out there?
Sorry but just a *bad* idea.
I can sympathise, as obviously the calibre developers have wowed you with what they produced to make you think all things should be so easily managed. But it is impossible to satisfactorily abstract and model "everything" in a common way without constraining and making an utter mess. Let calibre stick to what it is good at - the best book mgmt application out there.