A 3rd Inside Out film seems guaranteed, but whenever it it releases should be in less then 9 years from now. Sure it doesn't have to release in the 2020s, but it's best Pixar give way for other sequels that they might end up doing in the next 10 years from now, both with what has and hasn't already become a franchise. Something we can expect with a 3rd Inside Out film is that it takes place in Riley's college years, and that there'll be even more new emotions introduced, which I certainly hope can include positive ones this time around after the 2nd film for some reason only introduced negative ones:

*https://screenrant.com/inside-out-2-new-emotions-appear-sequels/
*https://theexploreist.com/guides/meet-the-emotions-that-could-debut-in-inside-out-3

Another thing that a 3rd Inside Out film should do is bring back Bill Hader as Fear and Mindy Kaling as Disgust, both of whom were wrongfully recasted in the 2nd film, especially after all Hader had been part of with Pixar and since Kaling was still a part of Monsters At Work, so much so that I'm also expecting a cut of that film where they get to dub over those that replaced them.