I'll upset some people and give my opinion: Every NFL team should be required to have a dome. Rainy and snowy games are fun on TV for a few minutes, but they decrease the quality of the football and are bad for players and in-person fans.
There are 285 NFL games per year, counting the playoffs. Let's have all 285 played under the exact same conditions so that it doesn't come down to luck of the weather.
Retractable dome is the answer for most cities. Football should be played in the elements, but the cities have to use them for other things like fights, concerts, and monster trucks to get their money back. In places like Kansas City and Dallas, the severe weather is just too common so a roof is necessary to attract the really big events.
Buffalo and Green Bay should just build open air football stadiums because that's all they really are. The big super fights and concerts are skipping those rinky dink towns anyway. The extra half billion for a roof isn't going to matter. You live in Green Bay or Buffalo you go to Chicago or Toronto respectively to see your Taylor Swifts and such.
Buffalo is unique because that whole city shuts down at times in the winter so nobody wants to schedule events there in the winter. I know Jerry World has something like 300+ events a year and a lot of them would not happen due to weather if there wasn't a roof. Probably not a lot of added value to add a roof in Buffalo that would be capable of handling the snow loads.