I wonder by what mechanism they plan to import these into the US. This seems like a emissions regulation end-run like glider trucks, but my understanding of the EPA import rules doesn't really leave any room for this type of game.

Yes, a lot of modern tractors are locked down due to predatory dealer service lock-in, but they're also complex and locked down due to emissions regulations, which are ostensibly a net societal gain. The classic HN "everything should be totally open and free" conversation really needs to happen through this lens IMO.