It's not an end-run around the process described in the Constitution -- just around how it has conventionally been applied.
Even the most liberal, revisionist USSC Justice on the bench couldn't say that Article II is ambiguous or vague in it's instructions on how a president is to be elected.
The Constitution is clear about how electors are allocated to the states. It is, I believe intentionally, silent as to how each state divvies up the votes allocated to it. It doesn't take a liberal, revisionist or even activist judge to see the distinction.
However, IMHO if that scheme is implemented it will be a disaster for the voters of every smaller and more conservative state that may sign on to it. They would in effect be compelling their state's popularly chosen electors to carry out the will of the larger states' voters, which in most cases would be the opposite of the small state's. Why would any state assembly do something that irresponsible if it accurately represents the political makeup of the state as it is presumed to do?