Finally have something to show off:
What you're looking at is a map generated entirely by a text file, and yes those are half tiles. Although I don't expect anyone to make maps in notepad, here's the script for the map if anyone is curious: http://pastebin.com/fMMR1Dt6
Once ECWolf is released a script such as that one would go into Doom wad file which can be loaded to replace the stock maps. The wad file may also contain things such as custom textures or even custom things. The release is still a ways out though since right now I still have much to re-implement. For example right now only static decorations can be defined (well they can animate but I don't have any code pointers implemented yet so nothing moves).
Edit: Almost forgot I wanted to mention that it should be possible to freely mix high and low resolution sprites right now. I haven't gotten a chance to get the Mac wolf resources to test it, but the sprite drawing code does take scaling into account.