What are your ethical concerns about this experiment? I don't think sheep with a human pancreas need to be treated differently from sheep with a normal pancreas, ethically speaking. We're not talking about fiddling with the sheep's brains.
I guess it's the sort of thing you can count on someone doing the moment it's possible...
That's an interesting idea. If it's OK to hire humans as surrogates, why couldn't we create an animal to do the job? Especially if an animal with a wider pelvis (e.g. a small cow) were used, it could eventually be made safer than regular human pregnancy.