An actual NFL franchise in England? That's the worst idea ever. I'd imagine multiple owners having issues with that, especially the teams that would have to play home and home with them every year. If they stay in the AFC south, that's a 9 hour flight from Houston. Not to mention if they get paired up with the NFC south one year, traveling to Seattle, San Fran, and Arizona will be absolute hell.
Imagine playing a Sunday night game here and then having a Thursday night game over there (it'd have to be played at 2-3 PM to air here on NFL network); there is not enough rest/downtime for that.
That'd be a worse idea than having a MLB franchise in Puerto Rico.