The fact that someone bothered to make uPnP suggests that there's a need for this capability for average users.
There's also a "need" for antigravity and wish-granting genies. They're just needs that may remain unfulfilled due to impossibility.
I assume since you bring up uPnP without citing it as a viable solution, you're aware that it's disasterous for security. I think at least some of that is due to inherent problems in the concept, not just a poor implementation.
Granted, we seem to have gone down that path already (perhaps driven in no small part by the prevalence of NAT), and these services may have a place, but do we want it to be *all* there is to the internet?
I agree that we want people to not be reliant on centralized servers... however, the way to accomplish that would be to upgrade the "average" technical expertise of users to the point where they'd be competent to configure a firewall. That may be practically impossible, but I think developing a technical solution capable of saving them from themselves would be even harder.
I accidentally left my Windows box connected to the internet without an external firewall for a few months with no ill effects.