I've recently read Rick Perlstein's Before the Storm about what led to Goldwater becoming the first national candidate from conservative wing of GOP and it was pretty enlightening on what happened.
Basically months before California, Goldwater already had enough delgates to get the nomination thanks to political operatives who wanted him to run going into each state at least a year in advance and taking control of the GOP on the local level to capture the state's delgates. Basically when the "Establishment" enter the state nominating conventions those in attendence were all for Goldwater because the system the "Establishment" had created had been used against them. The problem for the Goldwater camp when it came to California was that during the primary season he hadn't exactly been winning like a front-runner should have and everyone in Goldwater's campaign knew he needed to win because the convention couldn't nominate a perceived loser and stand a chance.
After the '64 convention, Goldwater's "Arizona Mafia" dismissed all the political operatives' plans and organization. Basically the campaign was a disaster because nothing was coordinated from the national level to the state or local level, the campaign would say one thing and the candidate would make a speech about something completely different. The reason Ronald Reagan got noticed was because campaigners for Goldwater in California essentially went, in today's term, "rogue" along with another states and organizations who supported the Goldwater campaign. Basically if Johnson didn't steamroll Goldwater it would have been his own fault.
If Rockeller had won California, he wouldn't have been the nominee but neither would Goldwater. I agree that Scranton probably would have gotten the nomination, but the enthusiasm the conservatives had leaving the convention wouldn't have existed and they wouldn't have been willing to do anything for Scranton.
The coordination between the national and state levels would have been better, but there wouldn't have been any people wanting to campaign for Scranton like there was for Goldwater. It might have resulted in Wallace entering the race and probably winning a few of the southern states that Goldwater did in OTL. But Johnson wanted to legitimize his entire political career with a victory in 1964 and facing an essentially divided GOP, he win handily.
What happens afterwards in this scenario? Reagan wouldn't have been seen in the last national broadcast by the GOP and thus doesn't run for office in 1966 and eventually become myth that today's conservative candidates try legitimize themselves. Nixon would have campaigned for Scranton like he did for Goldwater in OTL to be seen as a good GOP soldier and would campaign for congressional and gubernatial candidates in '66 like OTL, and he would have learned how the operatives for Goldwater had acquired all those delgates and used that system to get the nomination in '68 as per OTL. Goldwater would win re-election for Senate in '64, instead of concentrating on the Presidential campaign and not running for the Senate, and become an elder statesman of the party for the conservative wing that would be pissed off that their man was once again denied at the convention (Taft in '52).
And a remote possibility that the conservatives breakaway from the GOP to form their own party some time between '64 and today exists depending on when/if Reagon enters politics.