If type is Qt::BlockingQueuedConnection, the method will be invoked in the same way as for Qt::QueuedConnection, except that the current thread will block until the event is delivered.
The return value of the member function call is placed in ret. If the invocation is asynchronous, the return value cannot be evaluated.
По доке создается ощущение что даже с Qt::BlockingQueuedConnection получить результат не удастся