Our sprinters carry everything up to 5' x 12' substrates on a day-to-day basis, with plenty of room left over for more stuff. We routinely carry stuff up to 18' long. They wouldn't fit into our Econoline. These are the larger vans coming now, not the mini Transit Connect. Two different sizes.
If you look at the specs:
Height (high roof Sprinter (not even a max roof) vs. Econoline): 76" vs 51"
Cargo floor length: (Extended which we have) vs Econoline extended length: 185" vs 140"
Cargo Width: 70" vs 51"
It's just a better design- the old has to be phased out, we would never even consider another Econoline, but if they have the larger Transit, we'd for sure look at them.