There are already states that shouldn't even bother - How about half the western states? Campaigns are already limited to a few "swing" states and everything else is practically ignored. Your mistake is to believe that "big states" have some uniform population and would 100% go towards one party under a popular vote system.
And the popular vote can take hold sans constitutional amendment:
https://en.wikipedia.org/wiki/National_Popular_Vote_Interstate_Compact
With the nature of gerrymandering, I would loathe to live under system that splits any electoral votes based on Congressional districting.