Would it be possible to create a tab like that with icons for specific styles? Yes, it would. This is not a trivial task, though. From Graham's remarks I thought what they wanted was the classic menus interface. Again, I am aware of no version of Word that had individual icons, buttons, for each style. The Quick Styles Gallery is the closest.

I believe you would need an individual macro to apply each style and then have to assign the macros to icons on the Ribbon.

Here is the page on designing an easily shared customized Ribbon. It does not use the Customize the Ribbon interface but rather editing of XML. Customize the Ribbon (It doesn't take rocket science) by Greg Maxey, MVP