At the risk of repeating what others have already posted, if you think the peg is going to break on the downside, then the carry trade using HKD borrowed funds looks like a good bet ... assuming you can live with the risk that HIBOR/HKD Prime Lending Rates may spike as things unravel.
The Hong Kong dollar’s one-month interbank interest rate, known as Hibor, climbed 29 basis points to 2.42%, the highest level since October 2008. The jumping Hibor has helped narrow a discount to the borrowing costs on the greenback to the smallest since April.From Bloomberg...The Hong Kong dollar rallied as much as 0.12% to HK$7.8270 per greenback, its strongest since late December. Liquidity has been tightening in the city in recent days, with the one-month interbank borrowing cost jumping to the highest level in more than a decade Wednesday. Bears are also being squeezed by a surge in the cost of shorting the currency, as the local dollar’s 12-month forward points rise to the highest since January 2017.
HKD lowest is at 7.85 which will trigger the HKMA to buy HKD.
The recent incidence led to speculation that liquidity will be drained from hk market, i.e. the rich and scared will be drawing money away from hk and go to US/Switz/Singapore wherever else...
So when that happens, market foresee a drain of HKD.. then interest rate will go up..
that causes speculators that are betting on a weak depeg of HKD to cut loss and pushes further HKD strengthening..
so that's like what the market is speculating on the moves.. you definitely can find arguments against this. but the trader speculation, whether right or logical, are usually what drives the short term market and until it moves otherwise, will be deemed as the correct answer for now.