Look, if you have the engineering chops to turn out pro quality mixes, and master them yourself, it does not make all that much difference what DAW you are using for the most part. The issue raised by the OP was one that relates to moving your product to a "professional" collaborator/mix doctor or mastering expert. It may be quite true that many of the highly qualified people working in audio today are doing a lot of their work in a vacuum, and that they do not need the capability to share or open a full project in anything but their own favorite DAW.
It is also undoubtedly true that the days when song writers were using professional studios for making demos are coming to an end. The economics of both songwriting and studios, and the technical capability of inexpensive computer audio processing have changed dramatically. Since 2000 the number of professional song writers in Nashville has declined by 80%, for example, and the publishers who used to pay writers salaries and pick up the tab for demos are not the players that they once were.*
The ability of almost anyone to upload his music to the internet, regardless of the musical or technical quality, has dramatically increased the demand for affordable and easy to use DAW software. Many people who will never make a profit from their music now have access to quality processing that would have cost hundreds of thousands of dollars in the analog age. That is good news for Cakewalk sales, as it is for its competitors. Like it or not, many customers will choose another DAW that is less suitable to their needs just so they can say they have the "professional" software, as they might buy a shoe that does not fit their foot because their favorite basketball star wears them.
Cakewalk is an excellent choice for the DIY composer/musician/recordist. Historically, it descended from a first rate sequencer that added audio capabilities, as compared to many of its competitors that added MIDI capability to a primarily audio application, and it remains strong in the MIDI/softsynth area. Cakewalk has made impressive efforts to broaden Sonar's appeal to a wide variety of musicians, or pander to the latest fads depending on your point of view.
Nonetheless, there clearly is a group who are going to find doing their work in Sonar inconvenient when they are trying to collaborate with someone using another DAW. The money cost of Sonar is negligible compared to the time cost of learning to use a DAW, and the time cost and technical limitations of modifying a Sonar project to move to and from another application is not insignificant. I personally do not see myself as quitting Sonar for a competitor, but I do not interact with "professionals" in the audio world.
One issue to consider is that amateur collaborators may also need to standardize on one DAW. That could easily be Sonar, as there is certainly a large base of users out there, and there are very affordable versions available. But Sonar does not seem to have made major inroads into the academic music world. One does not see a lot of conservatories or music or recording programs in college building courses or labs/studios around Sonar. Many graduates of these programs, the very people who may be interested in collaboration, will have spent hundreds of hours learning to use another application. I suspect ProTools may be the academic favorite, but I do not have figures to prove it.
Many graduates will have purchased expensive software at affordable academic prices or as a "required text," for a course, which they continue to use for some time after graduation, and will likely upgrade that DAW. Cakewalk could offer Sonar on a ridiculously low monthly academic rate, say free, and require proof of student eligibility yearly to keep the subscription current, offering upgrade pricing to graduates. That would have some appeal for cash strapped students. Unfortunately getting an associate adjunct professor of music at a college to spend hundreds of unpaid hours, that could better be spent tutoring undergraduates in skin flute techniques, learning a new DAW would probably not be easy. And it is faculty, not students, who need to be made happy in academia.
*
http://copyright.gov/policy/musiclicensingstudy/copyright-and-the-music-marketplace.pdf