ARA architecture could be opened up and made to support midi, then a third party solution could add notation to any ARA-enabled DAW.
I use musescore without major complaints, and occasionally transfer midi files back and forth with Sonar. What advantage is offered by having comprehensive notation native to Sonar? Is it just so that you can use VST instruments for playback? Generally when I'm thinking in terms of notation, my process is abstract enough that it doesn't really matter what the instruments sound like - in the same manner as, I would guess, a composer in the 19th century might be sitting at a piano, conceiving of music for orchestra. (I'm a guitarist, so I tend to compose with guitar in hand when I want less abstraction without the option overload of a full DAW.)
My sense is that Cakewalk might gain traction by not just developing notation, but taking it further by offering multiple visualizations, either through the "edit filter" or ARA or something like the Step Sequencer.