I understand that .Net Framework and .Net are two different beasts.
You need to understand that this is a forum for Mathcad/Prime users, not the developers, not PTC personnel (although some of them sometimes show up here, and of course the forum is moderated by PTC personnel).
I've got a return question for you:
What does it matter to you how Mathcad/Prime is developed, whether in C, C++, C#, Basic, Fortran or APL?
What (do you think) you can do with the Mathcad/Prime application if it were developed using .Net ?
Especially, what could you do that you cannot do with the present options to use it, it's API and its interface for integrating your self-developed functions?