I think the biggest issue here is the matter of cheating. I play eldar, and the wave serpent (our dedicated transport) can carry a very vast number of models. I could have 3 wave serpents all with the same weapons and upgrades, and easly cheat. Okay so my first wave serpent gets destroyed, that one now is holding useless troops, but the one he didnt attack gets to now hold my fire dragons.
Okay so he moved his tank closer to my wave serpent that was holding DA's a second ago, you get to know have my Anti-tank troupes. So on and so on. It would just be much to easy to exploit in tournaments, and when it comes to being competitive, a lot of people will do anything to win. Heck a lot of people put a lot of time into this game, they would love to win.
If its with your friends, your obviously (hopefully) not going to cheat, then power to you, would be fun with secrecy and adding a whole new aspect to the game.
However, in any other situation, as a simplicity of stopping cheaters, full disclosure must unfortunately be in affect. Anything that can lead to potentially easy cheating has to be blatant to not favor the cheaters.