I think that is the point, chan_sip is not broken, but pjsip feels very broken, the problem is as end users we might not always have the option to choose.
It's not an immediate problem, but from the point of software security (knowing you can rely on it in the future) I would love to see pjsip working a lot better and more reliably than it is today.
I am not sure what other software uses the pjsip technology but I get the feeling it is better suited to supporting phones and soft phones than to pbx's and trunks, again maybe I have lost the plot, but at the moment I would rather see a future with chan_sip and not pjsip.
I don't know if other users have had better experiences than me with pjsip but when I have posed questions on this forum about its reliable implementation answers have been few and far between.