Let's say, ITTL, LBJ realizes the futility of continuing, and negotiates, leading to US withdrawal and a neutralized South in March 1965. What next?
The VWP(s) and VWP(n) as sister and brother both have a significant stake in whether the RVN is "neutralised" or "exists." Both of them were strongly, firmly, and engaged in 6 years of armed struggle (latterly) and 10 years of armed struggle (formerly). The former
as a matter of survival. So I am not seeing any plausible scenario where the RVN is "neutralised" in anything more than a dance of seven veils sense.
How is politics, both in the region
The VWP aren't going after Thailand. They're capable, barely, of going after Cambodia and Laos through proxies. Claiming a "regionality" to the war as a revolutionary or nationalist project is dog-whistling code supporting fascism in Thailand. Both at the time, and currently.
and in America/the Cold War changed by this? How is pop culture affected? Your thoughts?
Well pop-culture in revolutionary PRG Vietnam involves a lot less prosecution (persectuion) of Junkies and Whores. The Chinese ethnic community is probably
much less persecuted with 10 fewer years of war supporting the RVN elites. Possibly you get a softer, even
actual revolution under VWP(s) control. If everyone and their cat is lucky on Monday for three weeks straight. More realistically you get a different VWP(n) assertion of control over the revolution, which would involve less retaliatory nomenklatura persecution of comprador elites; but, correspondingly, a worse nomenklatura attack on VWP(s) revolutionaries and NFL operatives.
My thoughts are that America is not a determinate force, but, rather, a big fat jenga log jammed in place. All other phenomena wait for the jenga log to be removed. But it barely changes the texture of the social configuration; and, then, only to increase war crimes, excess civil mortality (paralegal RVN), heroin use, prostitution, and to increase the general tempo of blood. I'm not going further because all of the NFL PRG VWP(s) and VWP(n) are also liable for their state criminal activities taken outside of a rule of law; retaliatory or no: people died without nominal trials outside of military actions in a war "within" a state. The US certainly upped a tempo, and caused urban proletarianisation in a service (sex) work capacity. But it isn't as determinate as people make out. And everyone admits the South Koreans won the warcrimes attrocity award years running.
Neutralisation?
>Check out that 'Land Reform' in 1956
Check out how the party prosecuted those responsible for the failure of the 1956 campaign under popular complaint. Unlike many other early soviet elites, the VWP(n) was responsive: it held its own rule in higher regard than the positions or lives of its party members.