Good point.
I just can't see an NFL team ever really gaining traction in London, let alone England for that matter. In London alone, you have Arsenal, Chelsea, Tottenham, Fulham (since relegated), Crystal Palace and QPR in the Premier League alone. Plus, countless smaller clubs that still pull 15,000-20,000 in attendance on game days.
I can't see it being anything more than a novelty, but I'm sure the evidence supports otherwise.