Well, let's assume this occurs...
802.11n device released that can stream video:
-The current AE does okay with audio, because it doesn't consume much of the g's bandwidth (Airport Extreme). Only problem with it, is if you have b devices (Airport), the 802.11g spec will cut bandwidth dramatically so all devices can still communicate. Once in a while, you'll notice audio sputter/cut out.
-802.11n will most definitely need old compatibility with g and possibly b devices. Early reports I've read mention rather lousy throughput, meaning more than likely, crippled screen resolution for any video offered... I can't see much more than 320x240 with H264 if such a device is released.
Oh well, we'll know in a week I guess.