Wondering how long before they pick Wembley Stadium to host the Super Bowl...?
If it happens it will be AFTER a team moves to London.
The 32 people who vote where the game will be held, each have a stadium that they would like to host the game. Jets/Giants got support because plenty of owners of cold weather stadiums would like to host a game too, and there is a fair amount of horse trading -- e.g. you vote for my stadium this year, I will vote for yours next year.
You have some owners talking about it, but bottom line is each of them are more interested in hosting it themselves then seeing it anywhere else.
However, if there is a London based team -- then the dynamic changes.
There really is little to no upside to moving it. The games currently being played in London are of home teams that struggle to sell out -- so moving it overseas to increases revenue for the NFL. This has not been an issue for the Superbowl.
Other issues:
London games are played at 1:00 Est or 6 pm local time. Not unreasonable. The superbowl is played at 6:30 EST which is 11:30 pm local -- unreasonable.
Moving it would be very very unpopular. Politicians will take advantage of that. (b/c that is what politicians do) While the tax exempt status might not change. There absolutely would be congressional hearing into why the NFL is shipping the game overseas and if doing so should change their tax status. While nothing may come of it, you can bet politicians in every state with a stadium (which are the most populous states) will be using this for political gain.
There is very logical reason to move a few games every year overseas -- none to move the playoffs overseas.