John
To be candid I am not sure how this will benefit CW. It will be a boon to young musicians just starting out and don't have the money to buy Sonar up front. If I were in there shoes I would jump on this. Its a great deal. In the past I have passed up a DAW because I just couldn't afford it. CW has open the doors for all.
Perhaps by letting those that would like to have Sonar have an inexpensive way to get a Pro quality DAW they will get a lot more customers.
That is one thing they are hoping. The other is to get more people to buy more often. A problem that software companies face is that people will decide the tools they have are "good enough" and not wish to buy upgrades. Fine for the consumer, not so great if you are a developer who needs continuing cash for operations. With a traditional release model, each release has to be a big enough jump to get people to spend, and it isn't always.
With a model like this, they hope more people will choose to just subscribe yearly. That way, they get a continual stream of revenue. There isn't any particular milestone they have to hit, people will subscribe just to have access to updates and new features as they happen.
Also it helps keep the software more competitive. They can release new features as soon as they are ready, they don't have to try and bundle them up. That can mean that they can always be cutting edge (provided the development team can make that happen, of course) they don't run in to a situation where they are behind the curve because they are getting the next version ready, but some other company launched their new version.
We'll see how it goes for them. I doubt they'll say on the forum, companies are always overly tight lipped about financials. If you are interested, TEAC owns TASCAM owns Cakewalk so you can buy TEAC stock and sniff over their reports :) (I know Gibson owns the majority stake of TEAC, but it is still traded on the Tokyo Exchange).