So, what would happen, in a market perspective, is that both chains would start with the same value, but the one forked by Core (technically, Core would have to rollback, to reverse the stealing of Segwit outputs
Why would you assume they start with the same value? Did Bitcoin Cash start with the same value? How about Bitcoin Gold, Bitcoin Diamond, etc?
The Segwit outputs can't be stolen on the "Core" chain because that would violate the consensus rules. No rollback would be needed. The "Core" chain would continue normally like nothing ever happened.
That's why the whole scenario doesn't make sense. The Segwit outputs can only be "stolen" on a separate hard fork that copies the original chain's ledger. If history is any guide, the market will just treat that Bitcoin hard fork like worthless garbage. The only reason to download the client at all would be to dump your airdropped coins.