I guess I'll start by putting some thoughts down on the old ale...
Well, when you sell it like that, it's tough to say no.
I like the idea of a very simple grainbill. Between the yeast, caramelization, and aging, there should be plenty going on to provide flavor nuance without 100 specialty grains. they'd end up getting in the way of the real flavorful stuff. My guess is the brett used in the old ale blend will be fairly mild to moderate in intensity, so this isn't going to be anything like a lambic, for those who fear sour beer and bugs. At least, it ought to be if this is blended to provide an authentic English taste.
Boiling down the first gallon or so of mash runoff (to a quart or pint) would yield some good flavors, and make crystal malts superfluous, most likely. An overall 2 hour boil will similarly help (and also help of this beer is indeed 8+ percent). I sure wouldn't mind making it bigger than 8%, but I won't cry foul if that's where it stays.
I like the idea of mimicking an older, darker base malt, but many of the historical recipes call for chocolate or even patent malts in smaller quantities. My initial thought is I'd like to see either more brown/amber malt (maybe 1+lb of each, the better choice) or a small amount (4-8oz) of chocolate thrown in. If it's just the base malt, I get the feeling it might turn out to be a little light on both color and flavor. In an old ale, I always expect to find a dark beer, full bodied, slightly sweet, with dark flavors. Not roasty, but closing in on it.
Speaking of a sweetness, I'm also concerned a bit that a beer of base malts and sugars alone, fermented with both sac and brett might turn out a little too attenuated for a standard old ale. I'm not looking for syrupy, mind you, but I'm not looking for super dry, either. Will boiling down the first runoff change attenuation any? Can anyone assuage my fears on this issue? I suppose it could just be mashed high (154-6 or so), but would that prevent the brett from munching things down over the course of a year, or would it just make for a similarly low attenuated beer with a more prominent brett character? I can't say I've worked with brett before.
Hopping I imagine should be mainly or exclusively done with a bittering addition. Maybe a clean (i.e., not harsh) English hop like Phoenix or Target. Maybe even Bullion, as it would add some fleeting fruit (currant) notes that would meld well with the other flavors we're looking for. I have a feeling flavor and aroma additions may get in the way of other flavors and/or be lost during a period of long aging. For an 8% beer (something in the 1075-90 OG range) I'm thinking a 50-60 IBU addition should get us a nice, balanced beer after a year or so of aging. Yes, it will be a bit much at first, but this isn't going to be a beer that it intended for drinking at the 2 month mark.
So based upon what we've been discussing, here's a very rough outline for a 5 gallon batch.
12-13lbs Maris Otter
.5-1lb+ Amber malt
.5-1lb+ Brown Malt
1lb Molasses/Treacle
(maybe a small chocolate malt addition of 4-8oz)
50-60 IBU of British bittering hops (Phoenix, Target, Bullion???)
Mash at 154 or so?
Take first 1 gallon of runoff and boil down to 1-2 pints, add to boil
Boil 2hrs, maybe longer?
Use 9097 seasonal strain as preferred yeast
French(?) oak, maybe 1oz, in secondary (how long?)
Does this look like a tenable outline? Any major problems? There are details to tweak, clearly, but this seems to be coming together well, and I sure would be happy with something like this.
