I did look at the possibility of Jouno joining other organizations here but from the perspective of whether or not he’d actually agree to help Fukuchi. IF Jouno does later wind up joining the ADA, he may become eligible to join the PM through the exchange deal (albeit depending on timing, but I doubt Mori would take anyone in the middle of the climax). I do think that personality and even history wise, he’s in a very similar position to Dazai when it comes to “do you want to join/rejoin the PM?” He was also previously an executive in a criminal organization but has since learned the genuine reward and desire to help and protect the innocent masses (which Dazai learned from Oda and I’d be willing to bet that he’s learned it more firsthand overtime and believes it more now, since having joined the ADA). He probably also qualifies very well for filling Dazai’s empty executive seat, so in this hypothetical he could be chosen for that reason.

Ch 92.5, p 9, translation by @gold-pavilion

Ch 93, p 3, translation by @czkkn-upload

His sadistic nature does still stand, but it appears to now more so be both a general thing that he enjoys and something that guides him when it comes to interrogations, but now with the caveat of having learned the pleasure of protecting others. He’s still sadistic but he won’t be so nondiscriminatory with it, because he does care about protecting the civilians.

Ch 92.5, p 14, translation by @gold-pavilion

Also, Jouno being chosen in this hypothetical would spare Kunikida a lot of mental torture cause I wouldn’t be surprised if Jouno joined Dazai in messing with Kunikida if he stays.