Thanks for the link to their forum. Obviously, we need to update our Illustrator format support, but that seems like a separate issue to me. I would seem more topical/better to focus on a more direct link between the two softwares, if that is what is desired.
If Affinity does not publish a toolkit for their format (.afdesign), the obvious alternative is for the Affinity developers to use our free and robust openNURBS toolkit to read/write 3dm files from within Affinity. openNURBS is available in C/C++ as well as .NET flavors.