The main reason why a map editor hasn't been made is just because pokemon DPP and HGSS use 3d graphics, so making a map with those graphics would need a shat load of hex, for the shadows, dimensions and all that jazz.
Although some progress has been made in mapping, some people have been able to add simple things like flowers into maps, but I don't know know of anything else.
A few people have also managed to make scripts with hex.
So, if you really want to make a 4th gen hack, learn hex.
Of course I personally know almost nothing about hex and asm.