Since c2049f67e4cfe5f09e1b033b910cb37d043a287e in qtbase all underlying DBus stuff was moved into it's own dedicated DBus thread
KDBusConnectionPool was made before then.
QDBusConnection/QDBusConnectionInterface are very thin wrappers that dispatch into the shared dedicated thread. The creating factory,QDBusConnectionManager looks thread safe, it's certainly trying to do things.
I think there's a very very strong possibility whatever we were working around is not relevant anymore, but it requires input from whoever made this class.