I just had a bit of a brain fart on this reading up on the Red River collectivisation on wiki. The death tolls are low for a soviet-style collectivisation. The rent reduction and land redistribution pleased way more people than it pissed off. This, and the million refugees strengthened the DRVN politically. Party cadre were a primary purge target, which "cleaned house" after 1956. And the apology process certainly helped legitimise the party. It provided an economic basis for the DRVN's capacity to support the NFL without requiring the volumes of fraternal aid that the RVN required from the free world. A Northern Development line would probably not result in a similar collectivisation process. Correspondingly a kholkoz-type collectivisation would gut the economy. Either of these could leave an incompetent basket case with a pissed off agricultural populace, relying on foreign military aid to control a dissident peasant population. Which, of course, would be useless to help the NFL/PLAF. Which leaves the PLAF fucked by 1967 if the US intervenes in the RVN.
Maybe we should consider, "What if the VWP / DRVN leadership were as grossly incompetent as the RVN leadership?," as a way to resolve this. Only problem is you need a POD after 1956 to ensure that the DRVN/RVN form at all.