It was mentioned that Xara may not support the ability to switch the UI to the IMHO better original UI in future releases.

The logic being they could not afford to support two versions of the UI with the time required to create the various UI elements.

With many complaints of small scrollbars, small scrollbar thumbs, and other issues with the Code Jock skin (new darker UI) I would say it would be best to keep the UI as the original version. The developers are very familiar with it and would be easier to maintain.