How is this better then a filesystem with automated replication?
If I take a bunch of photos, those don’t have filenames (or not good ones, and not unique). They just exist. They don’t need a directory or a name.
So how are you supposed to find anything? Sure, I take photos. Most of them aren't needed after they serve their immediate purpose, but I can't be bothered to delete them, or sort or name the ones that do have a longer purpose. But at least they are organized automatically by date. For permanence, OwnCloud archives them for me automatically, from where they get sucked into my regular backups.
Why would I want to toss them all into an even less-organized pile?
[run] search queries over my higher-level objects. e.g. a “recent” directory of recent photos
How, exactly, are those search queries supposed to work? Sure, maybe date is retained in meta-info, but at best he is regaining the functionality he lost by tossing those pictures into a pile. If he is expecting actual image recognition, that could work anyway, without the pile.
It would be nice if we were a bit more in control. At least, it would be nice if we had a reliable backup of all our content. Once we have all our content, it’s then nice to search it, view it, and directly serve it or share it out to others
Sure, and that's exactly what you achieve with OwnCloud (or NextCloud, or whatever).
As for reliable backups, that's a completely different issue, which still has to be solved separately. You have got to periodically copy your data to offline storage, or you don't have real backups.
Seriously, I'm just not seeing it...
At least all the photos I take have a date and place attached to them. That is usually all the info I need to find them.