I think this would be a very helpful feature, seeing as how we now have the ability to make custom templates or whatever you want to call them onto the homepage of your guild and profile.
It would help to see what it would look like so that we don't have to go out of the editing page to see the results and go all the way back to fix any errors or something. Ya know, like the thread preview button. Because it's just "Reset" "Submit" right now with no option to preview the welcome message of the guild.