To be honest, I don't think it will ever happen. I may be in the minority on this - I don't actually want it to happen. The NFL should stay in the good old US of A as far as I am concerned.
I'm with you as well, i think a lot of older fans think the same way. Had a few arguments on the comment section of PFT as they often write some crap about us brits taking away a team and the usual cup of tea type stereotypical crap. I've posted several times that many fans dont want it to happen.
Newbies might love the idea of a London franchise but i believe most old fans wouldnt. I want the teams to stay in the US, yeah it might work at first but again the second that team goes through a few lean years the fans will stay away. I mean look at NFLUK and the fairweather fans there, New England hardly had any fans in the early 90's in the UK and now look, a lot of fans are fairweather ones who will just support a winner, the second the London Rams start losing they'll drift off.
Doing a game at Wembley once a year is still a great idea and its amazing when you look back to boring preseason games (which back then we loved !) at Wembley, i'm glad that does well but i think if they jump and go too far with a franchise that'll set the NFL back years as i cant see it ultimately working sadly