Part of the issue with transitioning from one feature to another is implementation and possibility of loss of features. For instance, with qleader/mleader we lose the feature of background masks on mtext. Mleader doesn't have a way to set the mtext properties's background mask by default so you would have to mask the mtext after an mleader is drawn. A little annoyance, that I hope others will be able to adapt to in transition. Other than that, if mleader is an evolution of the leader then it should be worth while to utilize it.