Given my very limited knowledge of how programming works, it seems that programming for Hamlet would be a bit more difficult than the other two DLCs. The main issue is obviously the indoor areas. Before I talk about those, however, I have suggestions for the parts that aren't indoor.

For most of the Hamlet world, just do it as you normally do, maybe have a custom skybox that emulates what is seen in the Hamlet trailers. For the forested areas, don't put the leaf effect on the top of the HUD, instead just make the skybox leafy all around. At night, just use the night skybox for all outside areas. Also have a custom skybox for Aporkalypse. One final thing: make sure that you can look up to see the BFB, as you need to know where the legs and head are at.

For the indoor areas, I'm not sure what entirely to do. The only thing I can think of is to just rebuild all the indoor areas, using only the front facing sprite for the doors and the columns and have new texturing for the walls, creating an area similar to that seen in Wolfenstein 3D. You might also have to transfer the flooring textures. All the other sprites should work out correctly from what I've seen in the current mod.

I know this is a lot of work, but let me know if I can help out with anything, as I'd love to use this mod in Hamlet.