Hello Sir Ivan,
A super useful feature would be this : you set your in and out points, and you'd have an "add marker from in to out point" feature that would do what your "add marker to selection" does, but for the in and out point range.
I use a lot the duration markers and there're really annoying to set up, you always have to drag the thing with your mouse, it would be so much quicker if we could do this with in and out points.