The NFL is perfectly happy with 32 teams. The only way LA will get a team is someone moving their. The Chargers seems most likely. However, they will have to build a new stadium, which thus far LA has not been willing to do for whatever reason.
The schedule and division alignment is perfectly set and made for a 32 team league. No change will be made to that number soon. And I don’t know what cities that don’t have a team now could support one. Some of the cities, even with moderately successful teams now, are struggling to support the teams they have due to outdated stadiums. That is the problem in Indy and Minnesota despite those two teams being near the top of the NFL this year. Its all about luxury suites and Club seats anymore. You need businesses in the city to buy the luxury suites. It doesn’t even necessarily have to do with individual fan support.
For the record, the NFL does not demand anything. The individual owners demand better stadiums and accomadations, but that does not come from the NFL itself.
The ratings for the NFL have nothing to do with whether LA has a team. Compared to other sports, the success of the NFL is very strong. Its probably the most popular of the professional sports in this country at the moment and has been for at least the last five years. I don't ever hear any NFL fans just dying for an NFL team in LA.