Comments towing with a recent Yukon 6.2L?

with modern electric brakes and a properly adjusted brake controller shouldn't the trailer handle a large percentage of its own braking needs?

In a perfect world yes. Accidents are usually caused by more than one factor lining up at the wrong time. For instance hitting a bump right before you need to brake even fairly hard can unload the TV's suspension and make handling vey difficult for a while. Couple that with dirt or mud or water on the road or a fatigued driver and there could be problems.

That's a lot of pulling and that little 6 cylinder with two turbo chargers sounds like a potential maintenance nightmare to me. They are too new to see how they will stand the test of time. I'd certainly get the best extended warranty possible.

One last point in the van's favor and I'll drop it. It has about the same footprint as the Expedition, just a lot more interior room without the hood. My family had one for years as a daily driver and it was no harder to drive than the Tahoe. Just twice the room inside. Your wife may be stuck on the cargo van idea but there are really nice ones too. You should at least contact a dealership and find a nice one and test drive. I think you would regret that many people and that much towing in an expedition.