Diesels are addictive. The more you mod them, the better fuel mileage they get.
My 6.0 SuperDuty got around 20 mpg with my romping the snot out of it and 12ish towing an enclosed trailer. Also ran a 13.9. Most importantly, it was a joke compared to the new 6.7. They are just plain crazy!
Never owned an EB truck, but I have the EB MKS, had a diesel SuperDuty, and had a 5.4 150 SuperCrew. If I could afford it, I'd trade in every ride I have for a new 6.7 SuperDuty.
Back to the dual fuel system on the new '17's, I think it's an attempt to improve the dirtiness of the DI set up. I suspect they will run smaller DI injectors for cleaner burning at idle and low throttle and then use the port injection for additional fueling when needed.
Sounds good, but that also means two entire fuel systems with potential for failure. I'm guessing they won't be a very desirable used high mileage purchase down the road.