Nope. If you're done in one HTTP round-trip, your HPACK state has to push brand-new headers, you benefit nothing from server-side push (if it's even enabled),

Nope. If you're done in one HTTP round-trip, your HPACK state has to push brand-new headers, you benefit nothing from server-side push (if it's even enabled), there's nothing to pipeline, so don't benefit from multiplexing and head-of-line blocking is a non-issue.