Stop the parties from nominating the electors?! My GOD man - who do you think you’re voting for in the actual elections? People the party put up for a vote that they wanted you to vote for!
First and foremost, we should be mindful that when the constitution was ratified by the states (thus bringing the fed government itself into existence), there wasn't a single presidential election day. Rather, over periods of weeks, the various states, by different methodologies reached agreements on how their state's electors would cast their votes. https://en.wikipedia.org/wiki/Election_Day_(United_States)
Development of the Morse electric telegraph, funded by Congress in 1843 and successfully tested in 1844, was a technological change that clearly augured an imminent future of instant communication nationwide.[4] To prevent information from one state from influencing Presidential electoral outcomes in another, Congress responded in 1845 by mandating a uniform national date for choosing Presidential electors.[1] Congress chose the first Tuesday after the first Monday in November to harmonize current electoral practice with the existing 34-day window in Federal law, as the span between Election Day and the first Wednesday in December is always 29 days.[5] The effect is to constrain Election Day to the week between November 2 and November 8 inclusive. Beginning with Presidential elections, gradually all states brought nearly all elections into conformity with this date.
With respect to this court decision, it's simply observing that the chosen method of enforcing elector compliance is unconstitutional; it is silent as to whether states can enforce electors by different methods/means (they can).
Secondly, this opinion does not address the current 'popular vote' compact of states either. That's a separate issue altogether, as it actually violates constitutional guarantees ensuring a republican form of government ie no direct democracy between states. (That in effect is why the compact will ultimately fail as well.)
So, we've come full circle where state appointed electors elect the president. The fail safe is they act in good faith according to political will within the respective state. That in turn is the responsibility of each state legislature, which in turn answer to the constituent power of the people.