The fact that the plaintiff is in federal court undermines the idea state legislatures can act without oversight. Moreover, the inability to review and correct bad law is the reason-to-be for courts. If the GOP gets what it wants here, how could they ever be a defendant on their own law about rules they used to get elected?
I am opposed to the aims of this action, but going to court to say "you don't own me" doesn't de-facto imply you believe they do actually own you: The court could say "yes, we agree" and the people who would be bound would be everyone else, who sought defence from the court system from the states corrupt processes.
As to the '2nd order effects' you are right: The defence of the gerrymander in some cases will undoubtedly depend on courts based actions to backfill the bogus designs given that no rational process can justify them, except to deliberately distort the intention of voting overall.
