I realize this thread is pretty old by now, but I wanted to post to raise a point. If we do go and allow the banning of abilities on Pokemon (Inconcistent, possibly Sand Veil / Shadow Tag), we have to consider that if the ability isn't the Dream World ability, we will also be restricting some of the moves that the Pokemon can learn. For example, if we were to declare Pressure a broken ability, and all Pokemon with the ability Pressure were forced to use their alternate ability, then for example Zapdos would not be able to use Heat Wave, as there is no way to obtain a Lighteningrod Zapdos with Heat Wave.
I'm mostly bringing this up for the inevitable debates soon to come if inconsistent is banned (which it looks like it will be) over whether or not its ok to ban certain abilities on certain Pokemon.
Another thing I wanted to ask - are we proposing to ban an ability as a whole if we find it broken, or just on that particular Pokemon (or whichever we prefer in certain circumstances)? In my own personal opinion, I think banning an ability as a whole would be more logical than banning on specific Pokemon (if it is forced to come to that), as that generally avoids confusion with ban lists.