I know that Brendan/Noah (forget which one) joked about Gladio being "another season" of Blowback in one of the episodes of Blowback S2, but I am curious what people would be most interested in.
I do think that a season focusing on Europe (either Italy and the Years of Lead specifically, or US covert operations in Western Europe more broadly) would be a good topic. Afghanistan would be very topical (specifically the rise, fall and rise again of the Taliban), but might be a bit close in content to their season on the Iraq War. I'd also be really interested in a season focusing on an African topic, such as the Congo, or the French/US operations in West Africa.
The militia movement in the US. The Vietnam war radicalized a lot of people in both directions and it fed directly into the white power movement in the US and a lot of reactionary people brought their training and military connections home. The Order and other militant groups grew out of this. Louis Beam and his cohorts were tried for sedition after a string of armored car and bank robberies conducted in an attempt to fund decentralized fascist radical groups in the US. There was a string of raids on compounds owned by these groups where the feds confiscated military hardware include rocket launchers and mounted heavy machine guns. What they didn't take was their computers and their online presence and use of shit like usenet groups to spread their ideology is directly related to the rise of the online alt-right.