I don't necessarily think exFAT needs to be implemented natively in any DOS, but should rather be implemented as an IFS/Network driver similar to the way CD's, NTFS, etc. currently are. At least in theory, that would allow any DOS implementation or version to use it.
I do think that hiding your head in the sand and pretending it's _never_ going to be an issue is not very productive for DOS end users, though. I can also understand nobody wanting to address it right now, since it really isn't a problem in today's environment -- but someday soon it will be.
Regarding the licensing/patent stuff, I'm not sure that M$ would even bother coming after anybody in the small DOS community for writing such a driver, especially if it was given away for free. It could even be argued that writing such a driver would actually be helping M$ rather than hurting them.
