Not meant as a necro, but I just wanted to point out that there has been a great project in the Dota 2 forum that was posted by invalidnick. He has a great little thread set up, and he has been consistent with providing updates, and even has documented the creation of the map via Youtube videos.
The thread can be seen here:
http://www.hiveworkshop.com/forums/dota-2-723/wip-curse-rivers-end-260456/
While the videos are by no means in-depth tutorials, they can at least provide the curious learner with some insight into how a great DotA 2 mod can be made. I still feel strongly that DotA 2 is where the most potential for THW 2 can be found.
Edit: Also, in an effort to get a little movement in the sub-forum, I compiled a list of various Dota 2 Workshop Tools resources that I found, and started a thread
here