Thank you for your feedback and sorry for my late response...
I'm currently modelling pieces which need to have an local coordiate system (timber members, where wood fiber direction has to be defined for example).
With such a geometry-attached plane , it would be easier to automate the process of creating oriented 2D-drawings of each piece, create BoudingBoxes, or whether display the main directions of each piece (length, width and height) with a gumball-like arrows-triplet (something similar to the "MPlane>Show" command).
MPlane as the big advantage to stay attached with the geometry and update itself by translating or rotating it.
Currently, the turn-arround I use, is to construct a rectangle curve grouped with the intended object. This rectangle is oriented and have a seam point: it acts then as a reference plane.
I was just wondering, if there were any other possibilities to do something similar as MPlane, but tougher than the "rectangle-trick"..