This scheme subverts the original rationale behind the electoral college; prevent the populous states from dominating the smaller ones. That rationale is well known and was made explicit in the Federalist Papers, IIRC. There are a lot of other aspects of the Constitution were the underlying rationale for one provision or the other is not explicitly stated. This is because the Constitution implements decisions already argued over and resolved in the proceedings of the Constitutional Convetion. Could or, rather, will such an argument support a challenge to this agreement before the Supreme Court?
Opinions about unstated rationales for constitutional provisions are not law. What matters is what the constitution says.
This plan still doesn't undermine that rationale anyway. Each state gets a certain number of electors, per the constitution. This is how the big state/small state issue was resolved. The number is determined by representation in both the House and Senate, where the Senate doesn't depend on population.
This does not change. Only how the state chooses its electors changes, not the number of them. States are free to establish any method they like.