Doubt there'll be a P5 manga anytime soon. The stress came more from the fact that he teased Chapitre 9 would be the final volume, but then had to apologize when it wasn't. And now he has to finish both the P4 and P3 mangas simultaneously, and is hoping he can get it done before P5 is out.
He's certainly been working on the P3 manga for quite some time. ANN tells me he started it in 2007. Almost up to 10 years now.