I think that if you are going to make a product like this, don't just focus on AirPlay. While it is nice, there are a LOT of other devices out there besides Apple. Heck, in the phone market, July showed the following market share:
Android 51%
iOS 32%
BlackBerry OS 11%
Windows Phone 4%

(source: BGR July 2012 Phone Market Share )
Sure, AirPlay is not exclusive of the iPhone by any means, but i nour house with a mix of Apple and Android devices, the Android ones are the ones that play the most music. For me using my Android phone, I either have ear buds in, or a stream to my home theater receiver. Having something elsewhere in the house for casual playback, but with quality sounds would be nice.

WiFi would be preferred over bluetooth to accomodate greater distances from the source to the "receiver" point for the speakers, but having both would have its advantages too.

Technologies just as DLNA would offer a wide variety of options for connectivity.

Than again, it is probably easier to cater to a single segment of the music steaming audience, but if you want to true attempt at audiophile sound for steaming audio, then it SHOULD cater to more than one market component.

Oh, and definately a wall-wart. Some people are going to do more "permanent" installs and will just leave them turned on. Even with a "sleep mode" to save power, the batteries wouldn't last long. Most "wireless" surround speakers are powered via a wall-wart instead of batteries for this exact reason.
2-M60s, VP180, 8-M3s, SVS 20-39PCi, DIY Sub, 8-Shakers, JVC RS45, Anthem MRX-1120