The first question I have with all of this (and the UK's latest Nonsense Paper) is who are we defending?
Taiwan? Ever since Nixon went to China the West has recognised "One China". Bit late to change our minds now?
Vietnam? The Vietnamese have beaten both the US and China in defending their homeland. Not sure what difference we could make.
South Korea? MadJong Un can do this one all on his own with a continuous artiller barrage on Seoul for openers.
Japan? Now we begin to get closer to reality. But surely if we are defending Japan, its back to W Germany in the 80s with a couple of Army Corps and loads of nukes forward based. Not sure the Japanese public would go for this one.
Sorry about the politics but without it you just have a lot of fancy videos and computer games.
The US policy towards Taiwan has always been unambiguous. It is obviously a weird policy, but the US has always underwritten Taiwan's security.
Any warfare in the Western Pacific will be largely a naval fight, along with copious amounts of aircraft and missiles. Outside of Taiwan I can't really see major landing operations by anyone in theater, and even that seems rather far fetched - the PRC can probably achieve its aims with a blockade or bombardment, assuming the US doesn't get involved or is defeated.
Bestest Korea likely wouldn't let the Chinese operate in the DPRK. Its possible the PLAN and PLAAF would want to participate, but IMO not especially likely. Phat Kim could certainly make a mess out of Seoul all on his own, but the Nork's ability to sustain that in the face of US air strikes would probably be pretty thin.
I don't see China having any ability to land in Japan unless the entire USN and JMSDF is on the bottom of the Sea of Japan, so I don't think additional US troops need to be based there under any circumstances.
And I'm all for giving Vietnam whatever maritime support they would like; when I was there got the impression they had a deep rooted cultural hate for the Chinese that far exceeded anything they felt about the US and French.