It also seems that he imported 4th gen maps into BW, so we know it's capable of rendering them. I'd say our next step is to find out all the coordinates of objects on all the maps and make a psuedo-editor out of that. Then, we figure out the more challenging things, and incorperate that.
And, to make it as complete as possible, it must be able to remove and add models on the map, rather than just move them around. This goes for both Gen. 4 and 5.
Edit: I have modified it to the specifications. I can't get textures working, but I got models to display. Attached is a modified PG4Map.
Edit 2: I found the .btx files for the title screen. It's located at root/a/0/4/9
Edit 3: I found some more .btx files. I found 4 similar maps of the 2nd area of Nimbasa City. They're located at a/1/6/6 and the .btx files are called 0_063.bmd, 0_065.bmd, 0_067.bmd and 0_069.bmd.
Edit 4: I have made a slightly better version that has less Engrish and has some instructions for usage.
Edit 5: Screenie of it using proper textures: http://img43.imageshack.us/img43/1567/pg4mapmod.png