Personally, I wouldn't *mind* seeing bitless bridles in dressage, though they seem to go against some of the more basic dressage principles which were established without the consideration of such a thing. Rules and regulations would have to be reworked, standards established, etc.
However, I think that in allowing bitless bridles, wouldn't one have to also allow things like jumping hackamores? Those don't seem to encourage steady contact with the hands at all (I could be wrong, I've never actually used one, and I will admit that experience in that field would be necessary for a fair assessment). It would also seem that if you're going to allow a bitless bridle that works much like a gag does [on the poll] wouldn't you then have to allow actual gag bits? Doesn't seem fair otherwise?
The equipment is not suitable for the discipline, and it is not likely that those responsible for defining the discipline would change their guidelines to accommodate some kooks. Why can't these wierdos just bugger off, invent their own "discipline" and leave well established and accepted practices alone.
The Majikal Bitless Treeless Shoeless Dressage Society.
If you're going to go "Treeless" just ride bareback.
I will say, it does do a good job of loosening up your upper leg/thigh/hip area to ride bareback *correctly* [read correctly as: horse going forward, coming through, rider not just letting legs go every which way, etc.].