California will eventually become a swing state - but the question is when. By default, given that Republicans must at some point within the next three decades expand their outreach to Latinos and other minority groups, California will become closer over time (or the Republicans are relegated to the minority status they enjoyed during the New Deal).
Let me try out a very far fetched hypothetical.
Whites: 50% - 62-36% Republican
African Americans: 10% - 89-10% Democratic
Asians: 13% - 54-45% Republican
Latinos: 27% - 38-61% Democratic
Result: GOP wins 49.28-49.22%
Very far fetched? Yes. Is there a very narrow path to California for a Republican? Yes. What's most interesting is that the white vote has dropped dramatically each presidential election. For Republicans to crack the Golden State, they need to expand their outreach and/or hope that minorities become wealthier and the party's social issues become less of an issue going forward. For example, Asians flipping to 61-38% Republican gives California a 2% Republican edge.
Obviously, Clinton will carry California by a healthy margin in 2016. This is merely a "thought experiment."
I'm three decades, California's demographics will look nothing like that.