Excellent analysis, as ever! The rebalancing/retaliation point is an important one. It's not obvious that many realise that the US was given a mandate by the WTO to retaliate against EU services exports in the Airbus dispute. That didn't happen in the end and other UK sectors were targeted. But as the UK is the world's second largest exporter of services, that is an obvious target if the UK does not ensure that future industrial policy is WTO-compatible.
I second Martin on the quality of the analysis. One very minor point for the sake of pedantry: there are no environmental exceptions to the subsidies agreement, uniquely among (major) WTO agreements. But I take you to mean that a semi-plausible political environmental justification might dissuade a challenge. On which point I tend to agree. The absence of any legal challenge to green subsidies (other than for local content reasons) to date indicates an unstated agreement, or perhaps just the motif of those in green (sic) houses not throwing stones.