This is exactly what I see as a great would-be time saver in terms of my day-to-day usage of Evernote! My Evernote is stuffed with notes on software development and a quick way to markup snippets of code (using the already existing font styles) is the only thing that is lacking in terms of usability.
Perhaps if a shortcut to a custom font style is to much to ask for, maybe simply a "reapply font style" shortcut could be an interesting alternative? Or.. implement/allow for the Mac style copying of styles using: