If your guess turns out to be true, that'd suck as I didn't go for the Signature... However, I believe it is unlikely the case since they need homologation for each market, and HK (RHD) and the Mainland (LHD) may require different configurations to comply with the local laws and regulations. If anything, HK and Japan might have more similarities in this regard as they're both RHD.
I think Mainland China is in a league of its own. It is, after all, the largest car market in the world with sales volume exceeding 21M vehicles in 2013. Tesla's entering into Mainland China hasn't been smooth and in my view it is still not clear when Tesla will be able to officially deliver the first Model S to a Chinese customer. Of course, for Tesla to grow big and succeed in the long-run China is a very important market. But right now, Tesla is struggling to ramp up its factory in Fremont, CA to meet demand in the US and Europe. Therefore, I think Tesla's plan into HK will not be affected by it's Mainland China plan, and there are reasons to believe we in HK will receive the car earlier than the Mainland customers.