I have very little data on this engine, but I must say, if they all performed like yours, it would be a boon for Ford!
The wear is incredibly low, the contamination nearly non-existent, and the oil characteristics (vis, FP, etc) all good.
17k miles easily; 20k is not out of the question by any means.
It's out of warranty, so there's not a lot of risk from that standpoint.
Absolutely no reason (other than typical fear mongering) to not extend out further. That is one stout little engine you have there.