Lofting between two different shapes along a path I want to model a tube-like structure, which slowly changes from rectangular to circular along a pre-defined path. Below is an example created with bridge:



There are two problems here. The first is that the tube does not have consistent thickness, and the second is that it is not possible to control the exact path of the tube this way.

Is there a technique, or an addon, that can help me out with this? I do not want to lay lots of manually half-morphed shapes along the way and use skin modifier. I have already tried lofting with LoopTools and did not get any usable results.
The Curve modifier might give you the results you are looking for and is added after the the loft. You can also sub-divide the curve for more control.