Measuring distance by two fingers is okay, but I think it collides a bit with zooming and rotation. Besides, we often do not need measure in the airline. If we are going to get some curves in the measurement now, we need to create a route and enter points.
My suggestion is to create a measuring tool where we only draw free hand line on the map and that this "line" is measured.
I think this idea is very useful, and it is hopefully too hard to implement. The problem is of course to determine how long the line is (maybe there is a library for that), but after that you only need to multiply with the map scale and voila!