Yeah; I'm quite aware of ERCOT's "independent Reliability Entity" registration at NERC, and recognized at FERC as such, BUT, believe me, when the FERC decides Mexico has a right to interconnect AND deliver power under an OATT (Open Access Transmission Tariff), you think Texas can stop it? ROFL
Power can already be sold across the nations and borders and has for many decades. Just not through ERCOT.
U.S. Electricity Imports from and Electricity Exports to Canada and Mexico
http://www.eia.doe.gov/cneaf/electricity/epa/epat6p3.html