But this effectively still requires a rethinking of the Bitcoin protocol, namely if the defense against a Goldfinger attack is to always soft-fork back to the original chain. And then one in theory has to determine exactly what reorgs constitute an attack, and what reorgs are just normal activity on the blockchain. Otherwise the community might disagree on a particular decision, which could thus cause a hard fork.
Not really, as it's pretty straightforward to determine: Does the chain include an adversarial double-spend? Reorg. No adversarial double-spend? No reorg.
Obviously actually pulling the hashing power to trigger a reorg would be no small feat in itself, but determining whether the chain is "honest" or run by the attacker is rather trivial.