Anyone that likes Plan 9 should also look at Amoeba [1] and Globe [2]. Amoeba did a lot of interesting work that could be considered when doing a modern, Plan9-like effort. Globe did for WAN's what Amoeba tried to do for LAN's. I had hoped solutions like Globe would get more traction given Globe applications would be way better than upcoming Web applications. Globe team even proved it by doing Web on top of their own stuff: doing Web better than Web lol. Unfortunately, the mainstream led us down a path resulting in trying to accelerate Web applications powered by protocols from time-sharing days on monolithic UNIX and Windows OS's. A little less fun...
Amoeba indeed had cool ideas, like most things A.S. Tanenbaum has worked on, but I always thought Sprite was more novel.
I haven't looked into Amoeba too deeply, I must admit, but other than its support for network transparency and single system imaging from heterogenous machines, I don't think it's very Plan 9-ish at all.
I'm glad you brought Sprite up. Been meaning to look at it closely. Far as Amboeba vs Plan 9, that was intentional on my part: get HN readers seeing something a bit different that happened in the same field. Probably just phrased the comment badly again (sigh).
Edit to add: The retrospective is definitely worth reading. I think most administrators, to this day, have it harder in some ways than people running Sprite due to their clever design choices in networking, storage, and single-system-image.
[1] http://www.cs.vu.nl/pub/amoeba/amoeba.html
[2] http://www.cs.vu.nl/~philip/globe/