QQmlProperty has a method connectNotifySignal that currently returns a bool, like QObject::connect also used to do. That is not very logical or consistent. It should return a QMetaObject::Connection instance instead.

Also, there are only two overloads, one taking a Qt-4 style SLOT and one taking an unclearly documented int (presumably the index of the method to connect to?). It would make sense if there would be overloads taking a pointer to receiver and a pointer to a memberfunction and and one taking a callable too, so you can connect to a lambda.