Don't forget, gear should go in the trailer. This way, only 10 - 15% will count towards the payload (assuming proper loading). But yes, payload is the biggest limitation on these vehicles. When I learned that I had an eight-seat vehicle that couldn't carry both eight people and a camper that could fit everyone, I was rather annoyed.
I'm not sure why Ford doesn't sell an updated Excursion. I think near the end of the previous model cycle it no longer sold well. I guess it's just a really limited market for people with many passengers and big boats/trailers. Once everyone that can actually afford it gets one, there's probably not a huge customer pool remaining. A HDPP option like what Ford offers on the F150 might be a better way to go. Most of us at the payload limit are just barely hitting the limit. Another 500 to 800 lbs would likely suffice.