We'll have to wait and see, as far as I can tell this "Axon Plus" version is brand new (as in today), and if anything it could be an April Fools joke.
The download doesn't seem to work, and the purchase page doesn't allow you to buy/select a quantity for Axon Plus licenses.
Anyway, I hope it is a joke because one of the best reasons to use Axon is the fact that it has always been a free product. I also think a big chunk of the revenue from Telephony products comes from users who download Axon, think it's cool and decide to purchase the add-on software packages like IVM, VRS, IMS and Quorum. By making Axon a paid product, I think it will discourage users from using it (instead of free alternatives like Asterisk), and NCH will probably lose out on potential sales that would have come from free Axon users.