I would love to have more modern version of Usenet. A simple news and commenting protocol that can be implemented in a web browser or a dedicated client alike. Something that is ubiquitous as RSS feeds. I have a client that aggregates all the latest articles from my favorite sites and and then can go in and browse comments in a tree like structure. I would have the ability to mark individual stories and even sub-threads to follow or know what comments I have read or have yet to read. Hell, I doubt that something like that would really be that hard to hack into RSS or design from scratch in XML.
Personally, I miss the early days of the internet where everything had a tool, and there was a tool for everything. There were programs and protocols galore: HTTP, Gopher, Usenet, Email, FTP, IRC, Archie / Veronica, Telnet for BBSes. Most of them are dead or so niche to be included only for "legacy compatibility". Now there is just HTTP to rule them all and shit is boring.