You guys are taking what's available now as set in stone as far as the Transit goes. Back in early June I attended the first Transit ride & drive open to the public in Kansas City, where the Transit is built.
There was a bunch of Ford engineers there that talked to us all and gave us a few hints of things to come, one of which was there were more versions coming along as time goes on. They would not say what or when. I took that to mean a T-450 and maybe a 550 (less likely) version eventually.
By the way, I drove 5 different versions, all vans, 250's & 350's & duallys, diesel and EcoBoost, loaded with 3500 lbs of cargo, and I can say I was impressed. I drove our 2013 Sprinter class B RV van over there for a back to back comparison experience which cemented my feeling that this current RV would be our last Sprinter chassis in an RV.
Another point, Ford is currently saying the E series cutaway will be available until 2020. The RV and fleet market for them is small as auto manufacturing numbers go, and being a 35 year auto industry employee, I'll believe it when I see it.......