I'm not so sure it'll have to be "free" but I suspect it will be. After all, you will be getting a more capable unit, which will presumably last longer because it is newer. You've gotten years of use out of the old unit.
Anyway, any offer will likely apply only to active units as of a certain date. No sense in making an offer and have all the old 6000s and unused 921s/811s come out of the closets for a freebie. Unless, of course, they figure they'll sell more programming that way and come out ahead.