We have heard nothing about any changes in Encore for CC. I would be very surprised if anything fundamental, like the preview engine, has changed. We really don't know what is still the old sonic authorcore, what may have changed but is still sonic, and what is Adobe created. I have always assumed the preview is sonic.
Is the audio sync issue Bluray only, H.264 bluray only, or any particular audio formats? I don't recall getting the issue in Encore DVD playback.