I could see this being useful, but it's not quite there yet. There are a few things I think it needs to support first:

    - comparing two fonts side-by-side
    - seeing multiple fonts/sizes/styles in the same panel so you can try
      to put together a whole title/body font hierarchy
    - alternate justifications--centered is not how I want to view body text

Until then, this isn't really a substitute for opening up a rich-text editor and doing it all in there, unfortunately.

(The text-editing component of this is fantastic though. I'll be very happy if this kind of thing starts making its way to more places.)