Whether this theory is true or not there is defiantly a fact that can't be denied, making these games is a HUGE toil for Sakurai, this has been the second time working on this series has seriously compromised his health, and in all these interviews he makes that abundantly clear that this job stresses him out more than any other, almost like it's getting to the point where he can't do it anymore.
Honestly, I think Sakurai should hand over the reigns to a new director for the franchise, not just for his own personal health, but with the direction he's taking the series I don't see what else they can do with it, SM4SH is the pinnacle of making a smash game balanced for fun players and competitive. While I love SM4SH I also don't think I'm the only one for the series return to form to Smash 64 or melee, very combo heavy game. They can still build a smash game that's competitively viable yet still have that layer of fun for the casual audience to enjoy.
As long as Sakurai is in charge he's not gonna steer it back that way, but then again this might be the last time he involves himself like this, which is sad, but necessary.