I think they probably know the unlikeliness of it actually happening now. I think the purpose is it advertise to the Congress and public just how unhappy they are with the leadership in California. In thr future, it could possibly be included in a deal to grant statehood to.Puerto Rico as "New California" would likely be a red state that could balance out a likely blue state (although Puerto Ricans aren't necessarily guaranteed majority blue, from what I understand). This would be the same model as the slave state/free state deals they did back then.