18 game seasons are both inevitable, and a bad idea. They would certainly need a 2nd bye week, plus to expand both the roster, and practice squads. But even then it's a bad idea, as QBs are likely to go down even more frequently than they do now. Imagine weeks, 17, 18, 20 when a winning team loses their QB, and are led into the playoffs with their version of Jarrett Stidham. Or tough guys like Josh Allen has a foot so badly broken he can't play. Plus the longer the season gets, the more likely players will sit, like they do in the NBA, where teams strategize losses, just to get to the "tournament" of the playoffs healthy. Fans will be upset if they are in a city like Arizona, looking forward to seeing someone like Lamar, or Allen come there and play for maybe the only time in their career, only to find out it's a "rest" game for that star.
I think what the NFL needs to do is plan to expand another 8 teams. Yep, eight. Four in Europe (England, Germany, Spain, France, or two in one of those countries, UK and Germany seem most popular), and four in the US (plenty of cities possible: St. Louis, San Antonio, Portland, Oklahoma City, San Diego, Salt Lake City, maybe even Toronto). AND have a second bye week. This bye week could do two things. Help teams travel to/from Europe. But also have one bye week the week before a Thursday night game. All this would take are a few billionaires to buy a franchise. And since the NFL basically prints money they are so successful, it wouldn't be a bad investment for any potential owner.