This feature is heading in the right direction but doesn't work that well. I started with free desktop, then upgraded to the $99 annual fee license and exported the desktop projects to my online accounts (which happened flawlessly, to be fair!).
When I copied a new version of a desktop page to an online project, the page was added to the online project, giving me 2 versions of the same page. This will create version control nightmare.
Moreover, the desktop file wasnt copied across completely. It was based on a Master. The link to the Master was broken, and had to be reset manually.
Not exactly synchronisation.