"The web separates endpoints into two classes: the "land-owning" pays-for-a-domain-name server class, and the disenfranchised client class where users live."
That's nonsense. Anyone can get a domain name for $5 and run a server for less. Users in the early web - usually not developers! - ran their own servers just fine.
The question is why they would want to? Especially given how big the web has become. They mostly would need applications that automated these details away for a broader purpose.
In fact many stil do run servers in their home in limited contests: their PVR, their backup appliance, their network printer, their Nest thermostat, heck even their Xbox with Twitch. It's all about the software application that warrants having your own server and makes it easy to maintain/run.
"Interactions between users are necessarily mediated by a server, which is why the economics encourage centralization. "
Its more than the interactions require software that needs to be written and evolved and maintained. A decentralized social network arguably has many benefits, that would lead to everyone buying something (software to run in their devices, or an appliance for their utility closet) to hook into it.
"You don't need "major parties" to "adhere to agreements" if users just use the software they like to interact with each other. "
The web IS all about agreements (protocols), as is the Internet. Decentralized execution of said agreements lead to emergent effects. Sure, if someone writes one piece of software, everyone by definition has agreement.
But the world of the network is about N versions of software written by different people and still achieving their ends.
Today we have cases of agreements enforced by single copies of software (Facebook) on a decentralized network with many many underlying differences in software (web servers, TCP stacks, firewalls, routers, databases). The only reason Facebook exists are the prior agreements made on those lower commodified layers, and economic value moves up the stack.
So why haven't we written the software and agreements to commodify Facebook? Because these things take time for the economic incentives to work. I believe it will happen, just a matter of time. The Web's architecture encourages decentralized sharing and manipulation of information, it's just incomplete.
" The problem with the Web is everyone using software on third-party servers to write rows in third-party databases because everything else is technically infeasible given the architecture of Web protocols."
What's the infeasible part? Where you see infeasibility, I just see "work in progress", or "incompletion".
"You need a DHT or some other kind of decentralized matchmaking service in order to actually connect users to each other."
Okay, there is a good idea for part of an implementation...
"At that point using HTTP makes no sense either,"
... And a bad one.
As an example - BitTorrent actually relies on HTTP and the web to bootstrap discovery to a tracker before moving to a an (optional) DHT. The web is an essential component of the puzzle.
"users don't have the time or resources to write complicated HTML or hire web devs to write it."
Why on earth would they need to? I can buy an appliance at Best Buy today that runs Wordpress for me. Why can't that evolve into something more sophisticated and compelling , that removes the need for centralized services?
I think you're way too hung up on this concept of a server being a socio-political construct rather than a transient architectural role in an interchange. Clients can be servers and vice versa. End users already run servers today, they just don't know it. The real socio-political construct of the Internet, the nexus of control, is the protocol. That's how you blow up centralized services.