That is a wildly unreasonable backup plan. Texas isn't gonna agree to split. California isn't gonna agree to split. Like the only state that might consider it is...Alaska? I don't know. I don't think yoconsidering what a massive undertaking that is.

It'd be easier to replace FPTP with something else. But if even that is too hard, the simplest solution is to just get rid of the electoral college. The popular vote is unaffected by state size and without the electoral college, "swing states" don't exist so campaigns would become more distributed across the country