Well, problem one - Delawares are SO new, that getting "good ones" to start with and getting anywhere near the Standard is not at all, anywhere NEAR simple. Ask anyone trying to make heritage quality birds, much less show quality birds. It will take generations of work just to correct and set type from any pure delaware stock had, just to make good delawares. Add another breed and you'd be looking at years, probably a decade.
Then there is that Delawares are a Barred Columbian, silver based bird. And crosses would be sex linked, initially and it would always be a hitch in adding in each generations best physical TYPE bird - because best physical TYPE (Murphy's Law of Breeding) always happens in the bird that isn't the COLOR you're looking for.
You'd end up forcibly wrestling your conscience - keeping that not so simple but much better Buff Barred bird, or that narrower, less typey, but better colored animal.
In the end it's a lot of birds grown out to at least 20-30 weeks prior to cull. That is costly. But until you see a Del's weight and feather and breadth at 20 weeks you don't know nothing about it, unless it's an early DQ. And 20 weeks is about the minimum, that's a lot of feed to raise even 10 birds, much less the 30 or 40 a season that would make "creating a breed" go more quickly.
I grew out my first 25 Dels in spring. I pared them down to 10. This Fall their first 10 chicks are on the ground. I won't know their quality til Spring. Then I cull the 20 back down to ten and hatch another 20 chicks. And that's just to improve the Dels. If I had to worry about also changing color, I'd go stark raving mad.
If you have the room and the budget and the decade and the patience - nearly anything CAN be done.
