Here's an opinion from a different angle:
One "UBoot bios and dongle besides some drivers" would be an easy task to port. Most libs and code can stay as they are. Sell a per-dongle license and let the rest be ported by who ever likes to. Also try to stick the license/payment to support/updates/docs rather than to the software itself. Think modern. Do it like the new generation of Music Industry. Look, SuSE managed to sell Linux for the price of a Windos while leaving the Linux itself free.