This is really not too different from what Microsoft is doing with Win 10.
I'm holding out for June 1 to hear how things go and whether I will cave and pay up :) I haven't gotten a new version of Sonar since X3 where I am today. I simply don't have the time to play like I used to, so beying a new versino hasn't been very compelling - looking for nuance when I can barely remember how to dock or undock a plugin! :)
That said, I don't agree with the Win 10 comparison at all. Microsoft does NOT rely on retail sales for Operating Systems for their major revenue streams (I recently saw a chart of 2013 and 2014 with Consumer OS sales being about 1%). The commercial (more like 50%), education, etc licensing along with the products like Office, big server systems like SQL and Exchange, Office 365 revenue, and other examples are the things that fuel the Microsoft fire. The Windows 10 model is a line on some accountant's book somewhere.
Cakewalk, on the other hand, has a few products and I have to imagine that one of the profitable ones over time for them has been the Cakewalk/Sonar line of things, with plugins and other upgrades being the extras. I see this as a way to get a large infusion of cash to do something big, like an aquisition that will pay over the longer term.
I can't wait to see what is coming. If the life-time subscription is not the bulk of it, what else they are going to announce should be pretty big.