It won't happen anytime soon.

DL's currently offering fares between SEA/PVG as low as $800 all-in, beginning in late summer. I've seen several consolidators advertise them for as low as $600 all-in - and you may be able to beat that price. The route appears to be developing quite slowly, and DL's upgauging it to the 330.

But I wouldn't expect more capacity to be injected in PVG.