I think SEA-PEK will never happen on the A330neo.*

*SEA-PKX, on the other hand...

All pedantry aside, this is probably the lowest yielding route Delta has out of Seattle. Mostly because they have to compete with Hainan, which runs an old BE Diamond seat in business - so fares are low and the competition is unimpressive. The 767 is serving the market fine, and I wouldn’t be surprised if it was years before this route saw suites.

Even more likely would be for DL to strategically toss SEA-PKX over to China Eastern, getting yet another new airline incentive and slot allocation from Port of Seattle and relieving themselves from having to fly the route at all. (Similar to how they have handled CDG, LHR and MEX). The main blocker on this happening is probably China’s one airline/one route policies, but there are some signs of possible liberalization happening there...