Things become generic if you stop defending them/enforcing your IP.
I think the iPhone at one time defended the design of its “squircle” corners. Eventually settling out of court.
I think you're thinking of trademark, but this isn't a trademark claim, it's a copyright infringement claim. The legal question is whether the guitar shape can be copyrighted.
I think you're thinking of trademark, but this isn't a trademark claim, it's a copyright infringement claim. The legal question is whether the guitar shape can be copyrighted.