Hierarchical organization

I think you're assuming tagging is harder than dragging it to a folder. In the Files app, it isn't. It's the exact same motion: select, drag, drop. Voila. (There's a "New" entry at the top to create new tags as well)

> I can shut out the rest of the world from my visibility, reducing clutter.

exactly how tags work. press on the tag(s) you care about and voila, the rest of the world is shut out from your visibility

> Merely copying the files serves to categorize them.

"default tag as part of the copy process" is one of the workflows we've sketched out but haven't yet fully implemented. it's pretty easy already, but once that is completed it will be as easy as your "copy 'n dump"

> Now, take backups. If I don't know where all my files are, how do I know
> what needs backing up?

files remain in your home directory. they aren't magically hidden in a wormhole between the sectors on the disk ;)

and for such backups, i'd recommend taking the metadata with the files as well. (well, for the metadata that isn't already in them, of course)

> UI can help with a dedicated backup tool,

all backup tools are "dedicated backup tools" in the sense you describe. except they are dedicated to raw fs hierarchy. i agree we need some spiffy backup/restore software (first syncing tools are landing in PA4, btw), but that will be no different than any backup software used.

the caveat indeed is that if you are using the metadata system, and then you want to go around and micromanage manual backups it won't be as smooth as it would be. that's a definite trade off.

the goal / assumption is that in the case of Active by using the system that, um, you're using you won't need to go to those lengths. which leaves your use case in the "edge case" category.

i will be the first to admit that the tablet interface in Active may not be for everyone. we're not trying to make something acceptable for everyone, because that usually means great for, statistically speaking, nobody.

if you find the semantic metadata system so inconvenient on your tablet (though i still suggest you may be surprised!), then i can offer a few options: don't use Plasma Active on it ;) .. or use (or make!) a more "normal" touch friendly file manager (i already know of one being written with QML, btw) ..

> but suppose some random app drops files in
> a location the UI tool doesn't know about

no such thing. all user-writable files are indexed.

> And if you plan on bucking the trend established by decades of computer
> science and hundreds of years of human progress,

ah, but you see here's where you're rather wrong. hierarchical file systems were designed for technical uses and users and within the limitations of computers (both in terms of hardware performance *and* in terms of data volume and variety). computer science has moved on some time ago from hierarchical systems. we merely need to point to google.com to find an example.

what hasn't changed is the implementation facing the user. this is particularly noticeable on mobile devices where there have been two approaches: ignore it and expose hierarchies all over the place; try to hide the file system and eviscerate the applications in the process (which you can get away with on systems that don't have high file management demands such as phones, at least for most people). mobile is a distinct use case from the desktop and the hierarchical systems just become more and more awkward there.

besides a couple decades of accumulated usability research to touch upon, we actually do user testing. at times that testing comes back with negative results and we adjust accordingly until we get positive results. so we're not shooting entirely in the dark, nor creating a self-serving echo chamber. we're probably more critical of what we do than most on the outside ... which leads to results that we are relatively confident about once they get this far :)

> you'd better have a pretty good flame-proof suit.

yeah, no problem there.