This is my first post here. I've been using CumulusX for a few months now and it has completely transformed my enjoyment of FSX and created a new passion for soaring.
I'm sure I would not be alone in saying I would stay or go wherever CumulusX development stays or goes. If it is a simple matter to port CumulusX to Prepar3d it might be worth it, as by all accounts they've ironed out a few bugs from the original code and got the sim running smoothly. I would not buy Prepar3d unless I knew CumulusX worked with it.
It's also worth noting Prepar3D does not include the DG808s, and I have not heard of anyone trying the SOAR DG or DiscusX in Prepar3d either. Might there be some legal concerns for independently porting these gliders across?
I'm very happy soaring in FSX but I wish the FS soaring community was more active. Browsing the threads here I feel like I missed an active period a few years ago. If implementing CumulusX in Prepar3D can stimulate interest in soaring then its definitely worth it.
So, not a very direct response from me, but I hope it helps a bit.