This is possibly a dumb question but I have a Qlik sense extension that I would like to see in QlikView desktop. Is there any way to convert the extension? Or do i have to create a new extension from scratch?
You can't currently just convert a extension between the two products, you would have to start from scratch. However a lot of the render logic that goes into a extension, which usually is somewhere around 90% or the code anyways, will be product agnostic and something that you could re-use between the two products.
That is an enormous oversimplification regarding support.
We support Extensions just as much as we support Loadscript, i.e we support the functions and methods but we don't support the script you create with them. So if you are comfortable writing complex loadscript using extensions in your app is nothing different from a support point of view.
Just as the structure of your backend data might change a browser might ship a new version which affects your extension. Actually Extensions are probably more error resilient than loadscript as usually 90% of the code of a extension is not Qlik related at all but normal, standard web technologies.