I've been thinking about how to build the dumb pipes/pumpkin spice thingy, and I'm leaning back toward a client/server architecture (or maybe plumbing is a better metaphor, but whatever). Here's my thinking, and tell me if I'm wrong.
First of all, second screens. I in theory use Tiny Tiny RSS because I want to be able to access it from my desktop or from my tablet or even from my sad little smartphone, though in practice I pretty much always hit it from the desktop. But Twitter I do hit from all my screens (totally not addicted, nope, nope). So I have to assume other people work like that, some even more than me.
Second of all, second screens that aren't second. A social network isn't (probably isn't) as important as groceries, but I still don't want to rule out people who only have sad little smartphones.
Third of all, and this might be an all-you-have-is-a-hammer, I have a whole lot more experience writing REST apps than direct-on-the-desktop stuff.
That complicates things a tiny bit more, but not without violating the you-are-the-customer, you-own-the-data principles. You pay your few dollars a month for a tilde-size server, you install Pumpkin Spice (a one-button install), you're in business. PS would have to be multi-user, so the technical member of the family could set one up and let everybody in the family use it (like we do with our TTR install).
One thing I think you'd need is an email address you owned, which tends to mean you have to own your own domain or you give up some portability. That also complicates things a tiny bit more, but domains have gotten pretty darn cheap, and again you could have a family domain.
Fortunately, I own enough domains and have a tilde-size server of my own that I can develop on it without goofing up tilde.club itself.