HSBC haven't yet announced their changes so probably best to hold off submitting an application unless you're chasing a sign up offer.
TBH HSBC's earn rates are already so cough that they could probably continue with them post July 1... 0.5/$1 is easily sustainable on the Premier and regular Platinum cards with HSBC Rewards.
With the Qantas Platinum card, the earn rate is also 0.5/$1 except on the first $2,500 of monthly spend where it's 1/$1, so that's only up to 1,250 extra points per month (over the 0.5/$1 rate) for the bank to buy, or 15,000 extra points per year. Assuming those extra points cost 1c each, that's a $150 cost that's perhaps not recovered via the revised interchange fee, against a $199 annual fee.
Boom, $49 profit - and even more so on cardholders who don't even reach the $2,500 threshold each month.
HSBC is also a more obscure bank to most Aussies than banks like ANZ, CBA etc... so most of the people who have this card are the 'informed' type who will likely have an AMEX too, and will primarily use their HSBC card for those times where AMEX isn't accepted - and more often than not, that's at smaller businesses (which will be paying higher merchant fees, even if capped at 0.8% interchange) than at larger businesses (which pay lower merchant fees due to volume), so most transactions are more profitable than via other cards.
Long story short, HSBC could make no changes at all and continue making money - especially now that they're not paying extra costs like buying Qantas Club passes which were removed a few years ago and get to pocket 3% on all foreign transactions (on top of international interchange) without awarding any extra points, which were also ditched along with those lounge passes.
