Melodyne 2.x is distributed as VST2.4 and VST3 and Rewire Slave
Current "integration" into Sonar is possible via VST2.4 and Rewire.
ARA is an extension to the VST2.4 AND VST3 interface. ARA is not "integration of melodyne", but extending the possibilities of plugins in general.
Both host and a plugin have to be able to "talk ARA". Currently, on the plugin side, only melodyne talks ARA, on the host side, only Presonus S1v2 talks ARA, and only within the "VST3 room".
The known "track based immediate offline editing of audio material melodyne style" is, what people usually mean when they talk about melodyne integration.
Therefor, Sonar has to be extended to talk ARA in general (then, when talking ARA in the VST2 room, Melodyne, and any other ARA aware plugin, could already be used ARA style. It's not necessary to build a new VST3 room within Sonar for Melodyne integration.