Dell has the 5k monitor but that doesn't mean that the systems they sell will be able to run it.
Most likely they'll sell it as an option for the Dell Precision line of towers that can handle pretty much anything you throw at them if configured correctly.
I was leaning toward the MacPro and the 32" 4K display, but the 5k iMac is seriously intriguing.
Yeah, I am on the fence about getting a nMP as I was planning until the iMac 5k showed up.
Most of my work is Photoshop, so while the 6 core nMP would be great for it, I could do very well maxing out the iMac 5k plus that display is awesome.
The only thing that makes me not jump on it right away is the fact the innards of the iMac will fade away faster than that amazing display. Heck I still have my 23" and 30" ACD after almost 10 years of heavy use. I feel would be a crime using the iMac for 3/4 years that is my usual upgrade cycle.