Just spoke with UA.

For the SFO-HKG route, you can buy H fares with an open return valid for 6 months, or an M fare good for one year.

Currently, H for November is $730 plus taxes, M is about $1420.

For the coach traveler, an H fare is about $100 more than a V fare. Since the V fare is limited to a 30-day stay, a longer stay requires H whether one wants an open return or not.

For we who upgrade, since we must buy H anyway, getting an open return means sweating the upgrade on the way back but would otherwise help avoid a change fee.

Maybe not always useful, but great if retired and want occasionally to spend an unspecified time in Asia.

Note that these fares and conditions vary widely in different markets