If that scenario is of your primary concern, remember what the US did to Pakistan while they invaded Afghanistan : they first got the Pakistani permission to use Pakistani airspace, albeit extremely forcibly. Nonetheless, the important part is that they did get the permission first and then enter. Also, the US provided Pakistan various weapons (ie. F-16s) and financial aid for using their air space and receiving "support" for the War Against Terror. When they did actually violate Pakistani airspace, it was clear that :
a) the Pakistanis are collaborating with Al Qaeda and was helping OBL hide in their soil.
b) Killing OBL was already a huge priority for more than a decade, and any possibilities of him being informed of the US raid through his connections in Pakistan government was unacceptable.
c) It was not a full-on invasion but rather a small-scaled spec-ops with stealth helos.
Now let's think about a case in which Indonesia will be put into in case of a conflict across Taiwan strait. Will the US violate Indonesian air space first hand? Probably not. Will the Chinese? We can't say for sure but I think they probably would. I suspect that the Chinese could resort to such tactics such as launching stand-off weapons from the airspaces of SEA countries. How will the US react in such cases? They would eventually need to engage hostiles regardless of if they are in neutral air space or not.
Well even they (both) don't intend to violate ID airspace they WILL eventually be forced to. A large scale war over the Taiwan strait meant that the US will use every possible assets in bases in the Pacific into the fight, ranging from Alaska, Guam, Okinawa and Australia. Previously the US had demonstrated their B-2s operating from Australia, for China the frontline in the Taiwan strait should be pushed as far away as possible. That means the Chinese will go after those Australian airbases near our Southern border. Just like they'll go after US bases in Guam or Okinawa.
They could opt ballistic missiles, but there's not really much to allocate for every US+allied airbases in the entire Pacific, not in a sustainable manner. So what they'll likely doing is go after those bases with cheaper and more mass produced stand off weapons. This applies vice versa for Chinese bases in the Spratly and the South China Sea in general.
Now standoff weapons like cruise missiles are aircrafts and they will violate our airspace. Heck, I agree with you that I don't think the US and her allies will wait until cruise missile gets near and prolly penetrate our airspace and go for the kill as early as possible. In the next decade or two, where B-21 and the notional Chinese H-20 enters service. The airspace above Indonesia and Malaysia in Particular will be subjected to heavy incursions by both sides.
The US (or specifically their USAF think tanks) has made it clear that they will disregard int'l law to go after China if war brokes out.
Hell, fellow QUAD India's airspace will likely be violated.
Now even if Indonesia opted neutrality, escalation in war could gets out of control, ID air force will have to make a choice if they're capable enough with the current state or they must push for a 5th gen fighter.
The difference in tech between a 4th and 5th gen fighter is akin as that of propeller piston engine fighter with a jet fighter.
If the US won't sell, we will have to find our own way.
. Don't mind me. Go on.
