Here's another quick thought: Has anyone started an RSS-Only blog yet? I mean a blog where there's no HTML version, just all RSS.
I have two types of readers: I have my subscribers who read my blog, come and comment regularly and occasionally link to me giving me decent search engine rankings. I have the other set of readers, those who find me via search engines and click on my advertisements and pay for my monthly alotment of gadgets. It'd be neat if these readers were one and the same, but they're not. My brief experiment with RSS advertising showed two orders of magnitude less money generated for that month with RSS ads: $10 vs $1000. We'll see if the new Google RSS ads generate any more money for their publishers, but I doubt it. People who use aggregators are also the people who use ad-blockers and know how to block images in Firefox.
Okay, that said - imagine if I got sick of the random people showing up at my blog leaving derisive comments and disappearing forever (even if they do pay for it). What if I just wanted my blog published to a community of people who felt that they liked what I was saying enough to add it to their aggregators and see it daily? Well, I could have a page that just said "Welcome to Russell's RSS Blog." and underneath there was an orange XML icon and that's it. Those who get it would subscribe, the rest wouldn't.
Now, here's a problem: Permalinks. How are people going to link to and follow permalinks? I'm not sure - maybe there'd be a public aggregator out there where you could refer to the unique ID of the post? Or maybe you just link back to the site, which gives you an RSS "snippet", i.e. a channel with just one item in it, but with an XSL transform at the top to make it readable to regular web browsers.
I guess comments would be lost as well, but you could just go with trackbacks. I don't like trackbacks much personally, but comments IMHO, are what is causing bloggers like Joi to get bored with the whole process. Commentors can be complete morons. For every few posts you read here I get one or two moronic or insulting ones (or both) as well which I don't let through. Makes me almost not want to bother sometimes. With an RSS-Only blog if you want to comment, then hey, use your own blog. Just like it used to be back when. Old skool blogging, baby.
I guess though that the loss of the search engines is pretty huge, not only for the revenue possibilities, but just the whole blog/search synergies. People find blogs through search, they then add them to their aggregator or point to them in their weblog, etc. It's not a coincidence that the rise of Google and the rise of Blogging happened at the same time.