A design team like Apple's.
Intel being purely just a foundry for someone isn't likely going to happen. That would be an indicator of Intel selling away the crown jewels. Intel is not a "job shop" and there is no way they are going to make margins like they currently do being one.
Just saying Intel already has ARM experience, maybe it's not current (especially since the StrongARM/XScale stuff is quite old) but it's something they've already pulled off.
Actually not. Typically when sell off the design and the product the key designers associated with the products also go along with it. When companies sell off designs along with people who did them. So they also tend to also sell off the knowledge in those people's head.
Intel has experience putting CPU oriented transistors on their process tech. But ARM specific optimizers they are not. They could give Apple tools/guides they give to their own x86 teams that aid in getting the most of out the process technology. But that would like Apple handing over sources to key components of iOS and OS X to Intel. That's not the way they typically do business.
Apple has plenty of cash, I'm sure they could persuade Intel into fabbing for them,
One reason Apple has buckets of cash is because they squeeze their suppliers. In other words, they don't spend money unless they have too. There are two other large and far more open Fab vendors out there. Waving their money at them would work much more effectively than waving it Intel. Because Intel is going to want much more money then those folks.
in exchange for a lucrative Mac long term contract for x86 stuff.
It is likely not in exchange but a courtship dance both sides are doing. We "could do" ARM stuff, but in the end it is really about exploring ways to keep the x86 contracts alive and growing.