Proportional electoral college voting would only lead to the House of Representatives deciding the election. With the ridiculous gerrymandering by the GOP controlled state legislatures, Trump still wins, even though he received less votes than Clinton. So the entire argument is useless as it doesn’t enable the people’s will to determine the next president.
If you read the linked article, you would see there is an alternative solution that doesn’t require a Constitutional amendment. If every state Clinton won enacts NPV legislation, it would only take Pennsylvania and Florida to join the group.