Hi Will,
Indeed, sadly Cargo Pilot won't work in W10 regardless of whether its a download or boxed product in any FS platform.
Downloads use different DRM so should be ok (apart from Cargo Pilot and other similar programs developed for use in WinXP) in FSX Steam Edition.
P3D is a different story though. Most products developed for use in FSX will need/or have been updating to be compatible with P3D (especially P3Dv4 onwards).
If you bought previous versions of the boxed products directly from us years ago, again drop us ticket and we can take a look for you.
Thanks,
Simon