Good question. Quite a few people seem to be, actually. Mark Lutter is one at http://freecitiesinitiative.com/. Patri Friedman, perhaps the most famous supporter of idea, attempted to start a charter city in Honduras but the Honduran government changed its mind (https://athousandnations.com/2012/10/31/future-cities-develo...). The Seasteading Institute, cofounded by Friedman, was once backed by Peter Thiel.