https://www.espn.com/nba/story/_/id/34854066/adam-silver-says-nba-monitoring-serious-tanking-issue-sources-say
"In such a scenario, Silver told employees, relegation would essentially mean demoting the worst one or two teams to the G League while promoting the best team or two from the G League to the NBA."
It sounds like Silver was not in support of it, but this would be an interesting way of preventing tanking.
I'm not against promotion and relegation per se. I think it works great in Europe and adds excitement and gives bottom teams something to play for. But it won't work in professional sports in the US because there's no history for it and because professional sports in the US are a franchise system. In Europe relegation and promotion have been around for a hundred or more years. There are multiple tiers of soccer that are run by national associations - in England alone there are 21 different leagues of football, from the Premier League down. There are literally hundreds of teams playing in tiers below the Premier League. Anyone can start a team at the lowest level and work their way up, nobody needs to approve their entry. And some become successful, like Leicester City - they went from third division to the Championship to the Premier League in 5 years and 2 years later won the Premiership with a Cinderella season.
In the US the owners are paying a fortune to participate in the NBA, with all the revenue streams that entails. Nobody would be willing to risk those revenue streams by getting relegated to the G-league. And in European soccer there is no salary cap - you can spend whatever you need to spend to get the best players to make sure you never get relegated.
About 11 years ago when American investment in the Premier League began to grow some of the American owners of teams (the Glazers and Man U, Stan Kroenke and Arsenal, and Gillett and Hicks and Liverpool) wanted to get rid of the promotion/relegation concept. Because when you're investing billions into a team, building new stadiums and everything else, you don't want to get relegated and miss out on TV money and all the other revenue streams that come with playing in the Premier League.
This argument still gets periodically gets brought up every now and then, but the game in the UK and Europe is structured differently. In fact that's one of the factors behind the European Super League that Florentino Perez of Real Madrid and Andrea Agnelli (heir to the Fiat auto dynasty) of Juventus were trying to do - to create a fixed league of twelve super teams (Real Madrid, Atletico Madrid, Barcelona, Juventus, AC Milan, Inter Milan, Liverpool, Man City, Man United, Arsenal, Chelsea, Tottenham) that would play each other in a league, franchise style, with no promotion and relegation. No crappy matches against bottom feeders, just the best playing the best and keeping all the money to themselves. There was a huge negative reaction to it in Europe and it folded even before it got fully off the ground, because the culture around sports there is different to how we have professional leagues here.
In Europe they like the idea that a club can work its way up over the years from League Four to the Premier League on the strength of its performances. But in the US professional sport is big business and no owner worth his salt would jeopardize their investment by agreeing to get relegated. It works well in Europe because the system is built around it. In the US it is not. They don't even have relegation and promotion in Major League Soccer here, because nobody would invest in a team with the expected expenses they would be asked to incur if there was a risk they would get booted to some minor league.