For my part, I want more long-form, thoughtful articles that offer an enriching read. Not only have we got a good decade or two's worth of experience showing that no algorithmic discovery system ever favors that kind of thing over content that's morally equivalent to Five Minute Crafts, but I've got a couple decades' worth of experience telling me that, since long-form bloggers tend to link each other quite a lot, never needed an algorithm to help me with discovery in the first place.
If I want anything, it's algorithmic filtering: Take the feeds I'm already subscribed to, and filter out the stuff that I tend to skip over without reading. Because my blog feed already delivers me a couple hours' worth of reading a day, so I can afford to be choosy.
For myself, I usually read in two "phases". I collect material from sources that are usually high quality for me, and do some superficial skimming to trim out the content I don't particularly care for.
Later, when I'm more "in the mood" or have a long period of time, I pop() and read(). The stack gets pretty large at times, but it only takes a couple days of vacation to blow through most of it. If I pass over something in the stack enough times, it gets free()'d.
I don't know if I'd trust an algorithm to do either of these stages for me. I'd trust an algorithm provide input to phase (1), but never to replace phase (1).
I think that Newsblur does this.
I appreciate people wanting to own their own writing, having permanence of data assured, etc. so this is probably worth thinking about. At the same time, many outside the tech world don't want the overhead of hosting or setting up their own blog.
I wonder if a hybrid would be best? Host yourself option or host-by-us option, with a pricing structure that accords.
The point is really to maximize ones ability to traverse between writers on subjects that interest you, so the physical location of the data is secondary.
I get that that would miss some of the benefits you mention (shared comment logins for example) but I'm wondering if people think it would capture 80% of the same benefits or, like, <50%. And I don't think for the discoverability to work there's any innate reason it has to be restricted to a single blogging platform.