I think the NBA's biggest problem is the drought in domestic superstar talent. It's a USA basketball issue at root level. But the way the NBA is covered by its partners seriously compounds the issue.
Guys like Haliburton or Edwards could have MVP upside (particularly Hali), but there are no Jordans, LeBrons, Kobes, or Currys on the horizon - and these guys used to drive the conversation 24/7. The best players in the league are international players nowadays. And they simply don't draw casual viewers as much as their US counterparts did in the past. The average viewer is not as invested.
The NBA nowadays is stuck in a dissonant state. It has historically been a soft power tool to promote a sense of American "greatness" (always an underlying message behind the individualization of the sport), yet its best players are not from the States. Against this backdrop, the league has struggled to reconcile embracing its international growth and appealing to a domestic audience.
And I think it's a problem that its partners - like ESPN - have been reluctant to embrace/sell Jokic, Giannis etc. as much as US-born superstars before them. They would rather shift the focus of the discussion to the Lakers, on KD, etc. and recycle these old topics to bring in short-term viewership. And I think this is counterproductive in the long run, because it diminishes the exposure to the players who are most likely to be relevant from a basketball sense. It doesn't help when chauvinists like SAS are prominent voices.
The league's other big issue to me is that these games have largely become unwatchable unless your team is playing (in my opinion). There's just too much stoppage of play. If there's anything to take inspiration away from soccer, it's the flow of the game, not a Cup format that makes conceptual sense in a relegation/tier system like the European leagues but none whatsoever in a closed system like the NBA. You'll never reach the same flow as soccer, but you can improve the watching experience by reducing the amount of stoppage of play.
It starts with implementing better video replay technology to lead to faster reviews . The NBA's technology is so far behind other sports, it's really embarrassing for a multi-billion professional league. I would also postulate - without any evidence - that the NBA has reached the point of diminishing returns with the ad money generated by timeouts. I think the number of timeouts just hurts the flow of the game too much, and hurts the viewer experience. I would look to trim the number of timeouts by a couple.
Finally, and I don't necessarily think this significantly affects viewership, but NBA officiating lacks transparency. It's incredibly opaque, the rules are too ambiguous, the refs have been enabled to take passion away from the game with these ridiculous techs, and overall I think the league has at minimum enabled officials to call games arbitrarily without any accountability. I find there is too much space for subjectivity in the way the game is officiated, and it hurts the league's credibility at least in my eyes.
Anyway, my bigger point is, I think the IST is a quick fix that will solve nothing in the long-run because it's devoid of actual meaning besides driving profit, and it addresses none of the issues mentioned above. And with the play-in tournament already introduced, it is now adding a level of complexity to the regular season that I find concerning for a legacy product like the NBA, and which I think will hurt the credibility of the NBA season in the long run.
We're in the honeymoon phase now. Novelty creates intrigue. Intrigue attracts viewers. Whether it's there to stay or not, I think this in-season tournament will be a net loss for the NBA in terms of viewership. But this won't be felt for some time. Maybe by then some of these more fundamental issues (imo) will have been mitigated.