Also: Bryan Bishop AMA, interview with Hub Dialogues
"I’m still researching this, but from what I can tell, the Extropian community sort of disbanded without directly accomplishing much..." Well, people in the Extropian community created Bitcoin, developed AI and neural nets, and many other things. They didn't use the term "extropian" but that's where they came from. So many ideas considered advanced and prophetic today were discussed on the Extropy Institute email list from the early 1990s. Extropy Institute was started by two graduate students (me being one of them) with no money. It's not the best way to start an organization. This was before Silicon Valley gave millions to organizations that grew out of our movement.
Many of us went on to do practical things related to and inspired by the Extropian philosophy but not known by that term. I went on to the run the leading cryonics organization for a decade. I also created the Proactionary Principle which opposes the disastrous precautionary principle. Robin Hanson is a very well known economist. Hal Finney and several other extropians created Bitcoin. Charlies Stross said that he got all the many ideas in his amazing novel Accelerando from years of reading the Extropians email list. Most of current transhumanism grew from the extropians. Nick Bostrom and Eliezer Yudkowsky were participants, among many others.