Almost, I'd probably try cutting the object into 3 pieces. Draw in 2 cutting lines in the top view and use them as the cutting objects in boolean difference to cut your object into 3 separate pieces.
Move the left piece over to the end location you need, and then use Scale1d to stretch the middle part out to meet it.
If you need a demo please post your .3dm model file or e-mail it to me at moi@moi3d.com if you want to keep it private.
re:
> 1/ single cut with a line boolean difference
> 2/ moving a part at the right place
> 3/ lofting between the 2 parts
>
> What do you think about it ?
> Right or wrong idea ?
It's fine, it's just that if there are a lot of edges to loft between that would probably take a little more time to do that than the 3 part method.
The 3 parts way needs just one stretch using the edit frame like this: