If you buy the WTP ticket straight from the booking page, you will be booked into W, E or T fare bucket (probably the latter if a sale fare) which are all upgradeable. The only fare I am aware of that cannot be upgraded is if you buy a WT ticket then later pay for an MMB special offer which books as a P fare which cannot be upgraded with avios.

Keep checking for availability. I have found it opens up in the last couple of days to HKG as long as the flight isn't full.