Look at the map, apparently everybody has an ADIZ before China declare her own.
China is exercising her right to do the same thing. How would that be escalation if everyone else did it many decades ago?
US send two B-52 to demonstrate their non-compliance to Chinese ADIZ.
Hardly surprising. I do not think US military feel it is bound to comply with anybody's ADIZ. The same for Chinese and Russian military that had never comply with US, Japanese or anyone else's ADIZ and demonstrated it regularly.
That is the international norm and most of the world military had the same attitude because ADIZ is unilaterally declared by the host country, and is not obligatory under international law. No military in the world would feel that it is bound by another country domestic law while in international airspace.
Those old and slow subsonic B-52 dinosaur flied on the eastern edge of the ADIZ, China monitored the plane and deem it not enough threat to warrant intercept. The situation is under control and there is no point in unnecessary escalation.
As we all know, US military planes do their probing near China regularly. This would not be the last of such event. Just why did the US decided to make it public, I would think it is mainly political. Probably they feel the Japanese need US to be the first to establish precedent in the new ADIZ, just why is that, beats me.