If I wasn't towing a 5th wheel and was towing a smaller 5-6000lb loaded TT I'd go back to a 1/2 ton. Better mpg, nicer ride and less maintenance than my CTD.
Most 1/2 ton owners don't pull heavy loads and IMO are looking for something that can compliment their other car. Most need room for 4-5 people and the use of a bed. Can't really get that in an SUV. You can do the Lowes/grocery store runs and do it in comfort. Hook up to a boat or TT and go camping on the weekends while still getting great MPG when going to work.
It's probably why the Ford F150 is the best selling vehicle every year. It's a jack of all trades rig.
How will the XD fit in? Don't know. IMO when Nissan releases the 2017 Titan with the gas motor I think they will have some good sales. The Cummins is just not that big of a deal to make the Titan a threat to any other truck brand.