The logic is the same regardless of how it is implemented. If the majority of electors are guaranteed to vote according to the result of the national(federal) popular vote, than all voters are equal, and it also then matters if a million people voted R in California or 10 million did (whereas today that is entirely irrelevant). And this all includes the voters of the states that don't join this coalition.

It may feel nice if your state casts its votes for your preferred candidate even if they lose the general election. But it is absolutely 100% entirely irrelevant rationally. And this is the only thing lost if the law change goes through.