I doubt Cakewalk will ever add an editor to SONAR (but who could have foreseen SONAR X). It is so easy to integrate a third party editor, there is little reason for Cakewalk to add it to SONAR. In addition to several excellent for-fee options there are a couple of decent free options, for example
Waveshop and
Wavosaur Pyro does add Red Book CD burning which may be of value which freeware editors do not have. But there are free solutions for CD burning too.