I am correct, that is it not possible to script dynamic extensions ( where you can draw with the mouse for example ) in Inkscape without writing a new tool in C++ and recompiling.

I can't find any Python examples which have that kind of interaction.

The video shows sometime I wrote a while ago in javascript.

Although I'd love to be proven wrong, I believe that "dynamic extensions" aren't currently supported.  I haven't found any examples, either.