GWX 2.1 was the last full version. 3.0 Gold is an update and finalisation of the cumulative work they did over the years. There are still things I would love to see incorporated, and individual members have made little add-ons that put some of those in.
The sad news, I'm afraid, is that they have moved on to a completely new world. The current project, announced even before 3.0 was announced, is GWX4, which will add the same feeling and depth to SH4.
As for the SDK, they have said that even with it it is too late to do anything more with SH3, as SH4 is the better platform to work on and offers even more opportunities.
And as for who they are, take a look at this:
http://www.subsim.com/radioroom/show...t=tribute+team
[edit] Oops. Unfortunately the link is dead. I still have a copy and will put it up tomorrow.