As described, an option that would alter the font menu so that the text you've written in your layer is displayed in place of 'sample' (in their respective fonts). It seems that this would make previewing fonts a bit easier than scrolling through one by one.
Thanks for your recommendation. It's something that we've talked about internally several times. The trouble is, allowing a customizable sample text would have a surprisingly large performance hit, which is why we've never done it. But, if there were a serious workflow issue that such a capability could resolve, perhaps I could make a case for it. Would you mind sharing what workflow problem this could solve for you?
Also, just in case you're not aware, if you open the Font Face dropdown and mouse over the various font names, you can previous how that font would look when applied to the current text layer. Would this feature address your needs?