I had also the idea with the mono dark run, I beated Keta(Only with very much luck...) and so on... I got till after the ghost gym then I sadly lost my savefile...
I also had the idea of an run with fire.
But I think this will not be this easy, I mean the battle vs the bug, water, grass and electro leader will not be this easy, cause of the rainy field...
Think the most succesful can be Psychic or Poison for Reju