I'll leave the merits of such a device for if/when it's available.
The problem I see is that Apple is shutting down these products today, forcing people to decide what to replace them with now. If, in a year or 2 they have some wonderful thing which does everything that Airport does plus Apple TV plus Home there will be people who have adopted a competitors system(s), and won't feel like converting back, since most of these music/streaming systems are not Apple compatible for whatever reason. In marketing this is the equivalent of
Look at the history of Commodore and the Amiga computer. Good product, lousy marketing and support.