Great points TBH.
The more I think about it the more Cummins makes sense. Not only is he a genuine wicket taking threat but he offers speed that Bird and Hazlewood don't. Those two are far more likely to bowl a consistent nagging line and length but they are the same sort of bowler. Starc proved in the first test that there is no substitute for genuine pace and a bloke who can bat abit at 8 is quite handy. If they bowl Cummins in short spells, like the did with Starc, they probably figure the risk is minimised and there's also very little of Pat available for Indian pre-game analysis.
That being said, it's more than likely going to be a pitch (road) similar to the second test so I'd expect our bowling unit to be looking at a minimum of 200 overs. If Cummins is the selection at 8 then I think Khawaja's chances are hugely diminished.
My thinking is that it would be a massive risk to take in Cummins without a bowling option at 6. If one of our spinners picks up a finger or wrist injury, or one of our pace duo breaks down, the remaining three bowlers would be forced to share the bowling responsibilities. Given Agar is the same sort of bowler to SO'K and that Stoinis is hugely unproven and inexperienced, we are left with G Maxwell - a bloke with experience in Indian conditions, a 'decent' first class record with both bat and ball, and a massive point to prove.