Drive values by Curves

It could be useful to have curves driving values, to extend the way the layout is defined. Instead of only defining start of clip, end of clip values, which is not very useful for every clip, to have :
- the values constant by default (no more pulldown "start of clip" and "end of clip")
- but the possibility to define a curve to change some values : only alpha but not the other...

The major reason : I would like to change the alpha for a clip in 3 segments : start of the clip, 2 seconds after the clip (linear increase), then constant up to 2 seconds before the end, then fade away linearly to the end. The only way to do it : cut the clip two times and define the 6 values, but when changing something, have to maintain the same values... painful.
And, not every clip require to define different values for start and end layout.

I would see an interest to change :
- the layout parameters,
- the audio volume,
- the speed, and rotation of the video
- and very important, the effect parameters.

So, I would see a button near every changeable value. This button, representing a graph, opens a popup window in which we can define a curve for the value : x = time, y = value. I have Blender's IPOs in mind (with only one curve per value). So: control points, kind of interpolation...