During one of my journeys around the remotely Quake-related parts of the web and IRC, I collected bits of info on the fate and current status of the BSP map editor.
Here's the history so far:
Yahn Bernier originally wrote the BSP editor. He was hired by Valve in the late 90s. I talked to Yahn recently and was privately given source code of BSP version 87b.
Yahn passed on the code to several people. One of these was Ben, who goes by the nick Sort and according to Lord Havoc was active in the Quakeworld community. Ben did many improvements to Yahn's code and also ran the website bspquakeeditor.com. Ben was pretty hard to track down, but Lord Havoc eventually dug up a working email address in an IRC log. Ben kindly passed on the source of BSP version 96d to me.
Ben also gave the code to other people. One of them is ViciouZ, a member of the Paintball 2 community. ViciouZ made a couple improvements upon Ben's source. Lord Havoc helped me to get in contact with ViciouZ via Paintball 2 developer jitspoe. ViciouZ also gave me the source of his improved version, cbsp 2.7, and referred me to yet another guy who works on paintball 2 Clan OTB's version of the editor, T3RRORI5T. I'm right now trying to contact him.
There is a loose plan by ViciouZ and me to start a repo for the BSP editor and maintain it.
I now have practically the latest source, except for Clan OTB's version. I'd like to eventually get this ported to Linux, for example.
Anyway it looks like we have another open source Quake level editor coming.
In other news, I spoke to Netradiant maintainer DivVerent about layer support. He came up with a possible way to implement it using group nesting and func_group, which wouldn't require any changes to the map format and no external files (unlike what DarkRadiant does). Div has put this on the TODO list of Netradiant.