3 things.
1. I haven't developed in C++ in AGES, last was 18 years ago and all of that on *nix platforms. A plugin would mean having to not only pick up C++ (and for that alas I have not the time at the moment) and more importantly to go read up on all the idiosyncrasies of C++ on Windows. Another can of worms I am not all that eager to get into. I should point out that I have looked at the code for both forks of the XHCWB04 driver here and got frustrated in no time flat trying to wrap my head around 4 different versions of MFC, 3 different versions of C++ (14.x, 17.x and generic) dialect not to mention Unicode or non-unicode libraries. That was quite enough for me thanks. Been working in C# on windows for the last 8 years (after some other stuff) and as such it made sense to go with that. I don't think however Mach4 plugins can be C# based (correct me here if need be)
2. I am not at present willing to engage in a non-disclosure agreement. This has nothing to do with NFS, more with the fact that I am currently employed in a rather strict work environment when it comes to conflicts of interest. Normally there should be no issue in me signing such an agreement but at the same time due to factors (that again have nothing to do with NFS) I can not discuss I am not willing to risk it either.
3. Taking 1 and 2 in consideration I decided going the IPC route, which is openly documented in the Mach4 documentation and as far as I can see requires no NDA. (again, if I am wrong here, by all means feel free to correct me).