Thanks for all the input!
I'm waiting for Jared to answer a few questions before I pull the trigger. Unfortunately, he was out sick for a bit last week and is just getting caught up now. Fortunately, the nice people at Madsen said they would honour the pre-order price if Jared doesn't get back to me until after the price goes up. (Other companies take note, this is how you are supposed to treat customers!)
Re: Wheel strength: It's good hear that they have a rep for being strong. If bike proves to be as useful as I think it will be, I'm going to to want to fit a dynamo, so a front wheel rebuild is going to happen anyway. I'm a big fan of Sturmey drum brakes -- especially how low maintenance and weather resistant they are. I suppose the other way to go is just to replace the front brake with Avid BB7, and then get a disc / dynamo front wheel built a bit later on...
I'm pretty sure that I'm going to want a bigger gear range than a 1x8 is going to give, so it's either a front mech, or a rear wheel with Sturmey 3x8 rear hub. I know the front mech is going to be cheaper, but in my experience fitting a front mech on a bike that isn't specifically desgined for it is usually a bit of kludge.
The big apple issue is interesting. I'm pretty sure I've read elsewhere that folks have managed to fit BA's (50mm) on their Madsens, but I don't recall if they had the wheel lock or not. Not worried about fender clearance, I've got a front that should work OK, and I don't mind fitting something to to back.
All in all, I'm looking to make the bike a low-maintenance and practical as possible.
PS: It's hard to be critical without actually seeing the bike, but I cannot think of a reason why the bike would't be designed from the get-go for clearance for fat tires. If nothing else, their resistance to pinch flats when heavily loaded should make it a no-brainer (or am I missing something?)