There won't be many games to be flexed Thursday Night Football, but the chances of it happening have grown with the latest rule change. The NFL used to have to make the decision on whether or not to flex a game to Thursday Night Football essentially a month before the game, 28 days to be exact. That notice has been amended to 21 days in advance. With more time to deliberate, the league should feel more confident about which games to flex.
There's a limitation on when and how frequently the league can make this decision.