I do not see it. Look at Puerto Rico where the preference for independence has withered being in third place behind statehood and status quo. As in PR, why would Mexicans in the Southwest want to give up the welfare gravy train or those with legal status the opportunity to move to other parts to the US.
today you are right it is far fetched. But conditions are always changing. As the SW Hispanic population, legal and illegal, continues to grow, a militant leader may well arise to rally the Hispanic population for whatever his/her agenda may be. The Hispanic invasion is out of control.
Puerto Rico is entirely different. They essentially are autonomous, running their own show, yet under the protective, nurturing (meaning monetary largess)care of the USA.