Good luck, folks:
The idea certainly makes sense in that rural California is sufficiently different from urban California that putting them all under one domineering bureaucracy is a recipe for massive mismanagement. But the likelihood of it happening? Approximately zero. The government of California would have to sign off on this, the congress of the US would have to sign off on this, and I believe a majority of the other states would have to buy off on this.
From the standpoint of those on the right side of the political spectrum, this would be a net win. If California was split like this, the total number of Representatives would remain approximately the same and the political breakdown should remain approximately the same. But if California was split in two, the current two Senators would become four. The current two permanently Democrat Senators would remain in Old California, but New California would have two of their own who need not be permanently Dems. This of course makes the idea palatable for Republicans, libertarians, etc., but the Dems are *never* going to go for it.
In the exceedingly unlikely event that it happens, the door opens for the same thing to happen elsewhere. The two most obvious possibilities are for New York State to separate itself from New York City, and for Illinois to separate itself from Cook County. Obviously there are liberal cities in conservative states who would like to separate themselves… say, Austin wanting to go their own way from Texas. But in the case of CA, IL, and NY, the situation is that a relatively small urban area is dominating a massive rural state, and those cities are big and populous enough to make decent states on their own. And of course Texas could always split up into, say, five separate states; again the representatives would remain approximately the same, but two Senators would become ten. At the moment most would be Republicans, but demographic shifts indicate that before too long a lot of them would be Democrats.
So… if Puerto Rico were to be brought in as a state, that would tilt the board towards the Dems. Split California, it tilts towards the Reps. The only way to do either, it seems to me, would be to do both.