"I'd be willing to bet that if solar off-grid living became popular that it would be made illegal to be off grid"

That is a sucker's bet considering there is already tons of precedent that confirms the government does this.  People who live off the grid are regulated, taxed and blocked by the government all the time.  (and in many cases like the OP suggests when people find a way, local governments change laws to make it illegal).  Just try fully disconnecting a home from electricity or water grids... they won't let you.  Provide for yourself solely off nature and barter?  Can't do that either.