Well yes, that's how it would work (and how it works on the current 27" DisplayPort based iMac). But just because you can physically connect a cable doesn't mean it will work as an external display. The connectors were the same on the old 27" and 21.5", but only the larger display functioned as an external display.
James
I hope it still works, I've been waiting for a speed bump before I buy, but definitely want to be able to connect my MBA if I need to