I always loved the Marvel comic book series "What If". The basic premise is that they took familiar characters and changed one thing like , "What if Norrin Radd never became a herald of Galactus?", then they had a little story exploring that possibility. I have some time before work so this is just gonna be a none fancy post, although i do intend to start making some words hyperlink, I think that is neat. So here is a what if for the Tau codex.
Drones didn't count against morale check casualties?
Drones were wargear?
Krootox were monsterous creatures?
The Kroot Shaper offered something other than a +6 armor save
The Ethereal was useful?
A Shas'el or Shas'O could be outfitted in an XV9, XV22, or XV88?
Pathfinders were a troop choice?
Firewarriors could equip jetpacks?
There was a flying transport for Crisis Teams?
a Sniper Drone team could be purchased as an auxiliary for a Firewarrior team?
Neutron blasters were assault 2?
Drones could explode?
Feel free to add your own What if ideas.