I'm still keeping the tilemaps in a custom format, as it seems like it would be more effort than it's worth to convert them to XML. I'm also not sure that I want to use tilemaps at all.
I need to actually sit down and write a full design document as i'm approaching the point where most of the base application framework is complete, but there is little gameplay yet.
Most of the gameplay is still up in the air - I still haven't decided if I want to make the levels by hand, randomly generate them, or do a combination of the two.
I'm also torn about making it realtime or turnbased, possibly a mix of the two, where it switches to turn based when you enter combat (something like the system Geneforge uses).