Extruding a shape into another along a curved path. Possible?

Let’s say I have a circle.
I have a curved spline that acts as a path.

I would like to extrude the circle so that after 15 extruding sections it becomes gradually another shape (banana shaped for example) and after other 15 frames comes back to the circular section. So the aim is to create a tube with modifying section.

As I said this should be done along a curved path.

Is there a way to do so?

This has been discussed years before (http://blenderartists.org/forum/archive/index.php/t-24083.html) but perhaps 8 years ago that feature was not present.

thanks for any help.

I’m not getting a picture in my mind what it is you are trying to do?
The best morphing tool is particle morphing tool. It sets a morphing key frame. Blender has curve deform and curve path.

Take a circular spline (not a perfect circle) and take another spline (a banana shaped for example).
I want to extrude the first for several steps along a curved path.
Every steps has to change shape in order to become a banana.

So I can get a changing shape tube.

I know there are other ways to reach the same target but I would liket to define start and end and make blender do the hard work.

Is it possible?

Separate the change from one shape to another and following a curve as two different things. The latter is simply using the Curve modifier.
To change from one cross section shape to another you could use the surface skinning options as mentioned in your link, the bsurfaces addon or use the bridge or loft function in the Loop Tools addon