The NFL is strongly trying to get all 32 team to have played a game in London. And all but 3 teams have... the Carolina Panthers, Green Bay Packers and Houston Texans.
The Packers haven't had a London game because there is no way in hell any team, under normal circumstances, would willingly give up a home game with how well the Packers fans travel (and therefore spend money)... but it might finally happen next season.
The NFL's two main ways of getting teams to London have been the Jaguars (who want to play in London as they seem to be considering a potential move to London) and the unusual circumstances of teams that are relocating and don't have their new stadium ready yet (such as Chargers, Rams and Raiders, whose new stadiums are expected to be ready to go in 2020).
So why could 2019 be the year the Packers finally play in London? Because they're scheduled to face not one but two of these teams (Chargers and Raiders).
The Raiders don't currently have a stadium contract signed for next season as their new stadium isn't ready and their old one is playing hardball since it's the last time they'll be getting money from the Raiders, so depending on what arrangement the Raiders have set up, this could be a great game for the NFL to move to London.
Meanwhile the Chargers are playing home games in a 27,000 capacity soccer stadium while their new stadium is being built. The Packers fans normally travel to warm areas Packers games (especially in winter) in huge flocks... 27,000 seats simply isn't enough for the crowd they could get and maximuming the games potential crowd. Meanwhile, NFL's 2018 London Games achieved an average attendance of 85,031 including a record attendance of 85,870 to watch the Eagles/Jaguars game.
As we all know the NFL likes setting and breaking records, and with the Packers fans that travel so well, the NFL will probably try to break the London game attendance record. So I'm fully expecting the Packers to have a London game next year, and I'm thinking it will be Packers vs Chargers.