I think the main problem is that ordinary people don't even see what problems self-hosting is supposed to address; and those that do, still need to dedicate significant time and effort to "tinkering", even when handed a huge chunk of the solution on a plate.
Another huge problem is that there's a home network between your product and the user's other devices; most home networks are utter crap, and often even tech-savvy people don't have a whole lot of control over it (I hate my ISP's modem with passion). This seriously limits your potential to provide an excellent UX; IMHO it's the UX that makes or breaks a product for "the rest of us".
I used to self-host a whole bunch of things on a VPS, including my blog, git repos, a DIY blogroll / RSS reader, etc. In the end I've decided it was not worth the effort; the blog was moved to Netlify, repos to Github, and the RSS kludge got swapped for NetNewsWire with iCloud sync. I was paying €5 for the VPS, yet now I'm paying Apple €20 to host my email, sync my photos, get access to the music catalogue, etc. I would definitely pay €20/mo for a box under my desk + an online service, provided it gives me similar value without much additional effort.
I think the problem that KubeSail/PiBox is aiming to solve might be both too broad (run any software you like!), and too narrow (if you're an enthusiast!) at the same time. I don't want to run Miniflux; I want to have my RSS feeds synced between devices. The software that pushes the bytes (and the hardware it runs on) should be invisible - unless I decide (out of my own free will / curiosity) to pop the cover open and start tinkering.
I don't think you can solve this by addressing shortcomings in a single piece of the stack. Both the layer below you (your average home network), and above you (the apps) have their own problems; some are like splinters (tiny but enough to ruin the experience), some are fundamental ("what is MySQL and why do I need to know"). I don't think it's a lost fight, but I would try to start with a vision for a more vertically integrated solution; maybe one step of that road is to eventually build your own WiFi AP/router (or even become an ISP), maybe to make a deal with Spotify (or even directly with EMI/WB/etc)... I don't think a task is too big if you can seriously challenge Apple/Amazon/Google at the end of the road.