This isn't such a narrow decision that it only applies to a specific case of not following the states voting choice. The decision holds that states have complete power to choose how their electors are decided, so long as the Constitution doesn't otherwise exclude that power. So, if a state has a law saying the state will choose electors based on the winner of the national popular vote, this decision holds that the electors must vote for that person or they can be removed.
There will certainly be more challenges to it later based on interstate agreements, but that will not stop it from happening since it's not really reliant on that. A state can clearly write a law with the provision that it not be enforced until a certain point, such as when enough other states pass similar laws. This decision will prevent any electors from arguing that they can not be compelled to vote for the US popular vote winner.
I know conservatives are crowing about this, although a faithless elector has never actually hurt them, but it's a win for us.