Sears/Compco said anything not protected by patent copyright etc is not subject to state anti-copying protection. Goldstein says Sears/Compco didn't mean that exactly- rather, states can't control copying where fed statutory policies would be in conflict with the state protection. Section 102b and generations of copyright cases say ideas, systems, etc., are not copyrightable. That wd seem to suggest that even under Goldstein, ideas, etc can't be protected against state law. However, a 1 iteral reading of 301 might suggest Cong decided there should be no preE of such state law protection of ideas.
Wendy J. Gordon, MISC Re Paper: Property Preemption (1990) (unpublished manuscript).