Video Editing features would be great. Right now I use Sony Vegas 13. and it does everything I need it to do. Once the video is edited I typically export it as a mp4 and then bring it into Sonar. At that point I work on the sound track. Then I export the soundtrack and bring it back into Vegas for the final render.
If Sonar allowed for video editing it would be great, but I don't know how long it would take them to match the same quality of editing you can achieve with Sony Vegas or even Adobe Premier. If they put simple editing features into the Sonar, I don't know if I would actually use them.
I don't know if I could achieve the same quality of editing like I can get with Vegas. There is a lot of code and resources that could be spent in other areas. It would also require a ton of bug fixes and versions to get up to speed with Vegas. Common Features like transitions and green screen effects may work for those who have no editing software.
I do like the fact that cakewalk has allowed different video formats to work inside of Sonar in X3e. I use to use avi formats until Sonar expanded the amount of formats that would work.
I would be happy if Sonar allowed me to render the video and the soundtrack together in a variety of formats and resolutions. This would save me extra steps as I would not need to export the sound track from Sonar and bring it into Vegas for render.