I have to agree with this. A big old ale sounds great. I've never had a beer with brett, so i might have to hunt one down to try first, but it certainly sounds like it would be amazing.
The brett is the main reason I am not too concerned about the grain bill. When a very clean ale yeast is used, the individual malts are more noticeable than in brett beers, at least to my tastes. I am not saying necessarily that brett dominates the beer, but it seems to blur the differences in the malts. As for hunting down an example to try, you'll mainly be looking for Belgians, as commercial old ale examples I know of do not have brett. Try Boulevard's brett saison, Ommegangs's Bier de Mars, or Oval. Since these are all Belgians, you have to imagine the brett influence in an old ale, I guess.
Anyone know how much the caramelization will darken the beer? Using 4% brown, 4% amber, 3% treacle only gets it to 13 SRM without accounting for the caramelization.