Thanks, Asif. I did say I hoped that, if they implemented this, Devon would make note-folders and proper-folders visually distinct. In fact, I’d go further: please, Devon, if you do this, allow a preference to turn it off for those of us who regard allowing notes to be folders as a step backwards. If that were done, then I guess I could have no objection to the proposal for those who really want it - although I still regard it as muddled thinking, as I shall explain.
Here’s my picture of the world. We see a number of different types of hierarchies in nature. One of the most common is what might be called the container-hierarchy. This is where the individual elements of whatever you’re studying are collected together in a group, and the groups are themselves collected together in bigger-groups, and so on - but where the groups (or groups of groups) aren’t themselves elements. In short, the container is a different type of thing to the contained. For example: a book called the short stories of Arthur Conan Doyle is not itself a short story by him; the entity known as the Beatles is made up of John, George, Paul, and Ringo, but is not itself one of them or any other person; there is no such animal as a feline - only cats, lions, tigers, etc. To mix these levels up is to commit what logicians call a “category error”, and it leads to many wild goose chases in metaphysics and elsewhere.
The container-hierarchy is the natural structure for classifying things; and this is purpose of DT, at least for me.
Another type of hierarchy might be called the tree-hierarchy. This is where nodes still contain (in some sense) those branches below them, but now they are of the same type. Examples are a family tree, where all the ancestors of a person are themselves people; or a flow chart, where the steps to be done are all still steps, regardless of where they are on the page. As these examples show, tree-hierarchies are primarily concerned with process, or one thing following another. There’s a sense of movement or flow of time from the top to the bottom. There might well be a place within DT for these type of object; but it is not DT’s primary purpose. (There is plenty of other software that does work like this - my favourite is Flying Logic.)
Now, normally, these types should be kept logically distinct, but it is interesting that very powerful theories sometimes make links between them. For example, Darwin saw that the container-hierarchy of living things (Linnaeus’s system) resembled a tree-hierarchy; and he posited that it resembled a tree hierarchy precisely because it was a tree-hierarchy. That, in a nutshell, is the theory of evolution: “feline” isn’t just a group of animals, but itself corresponds to a real (though extinct) animal, the ancestor of all modern felines. So, there is a use for mixing the two hierarchy types - but to do so is to put forward a theory about the way the world happens to be. It can’t be done just on a whim.
All this is just what I think about the way we should organise the world, and obviously other people will feel differently. That’s fine with me, providing, as I say, Devon gives me and others like me the opt-out on this feature.