Meh. I'm sure military circles in Beijing are considering future implications but I'd hardly call "The Quad" a nightmare.

India's military is an absolute shit show and India itself is extremely politically unreliable. Not only that, but in the event of a war China could rely on Pakistan to open a second front with India, which India would struggle to defend.

Japan is constitutionally bound from declaring war, has a population that is extremely anti-war, and basically has its hands tied unless directly attacked.

Australia is too fucking far away and lacks the power projection capabilities to get much done on its own.

America is going to be hostile anyway. This changes nothing.

Personally, if the Quad does solidify into anything, it'll only spur Russia and China into forming the formal alliance that they've been heading towards but dancing around for years. That alliance would likely draw in Pakistan and Iran, in addition to many of the central asian countries.