So I see now that there is much going on with regards to a potential RR sequel. Despite that, I have my own project I started a few weeks ago that I'd like to show off.
It looks terrible for now, but a lot of the foundation is there. First get the Visual Studio 2012 Redist (x86) then you can try it yourself. I wrote it from scrach in C++ using SDL2 and OpenGL 2.1, so while this build is only for Windows, it could easily be ported to other systems in the future. I plan to go into game programming and I learn best by diving in the deep end, so I started this project to learn C++ and have something to show potential employers.
QWERTASDFG control the camera, Z and X will destroy two hardcoded walls (to show real-time collapsing and exploration), CVB will spawn objects under the cursor.
Everything can be selected, raiders can be ordered to move to a location with a right click.
I'm not insterested in hearing the many ways you can crash the program, but if any of the above features don't work for you, let me know.
As for the map file, it's an ugly but effective text based format. Designed so I could make maps by hand and expand features without breaking old maps. The parser is extremely stingy and will complain about anything, but it should all be in the console. Use Notepad++ and watch your end of lines if you want to mess around.
I'm going to need some help with the non-programming stuff later. I hope to be able to import the original RR resources (if you own the game) at some point, and could use input on other features as I add them. Right now though, if anyone does want to make a simple map editor/creator, I would appreciate it.