The USB connection sounds like the elusive white unicorn....
I would love it if they came out with a cheap way to connect via usb to the factory stereo. But, I really don't think it will happen. If they do, I very much doubt the factory stereo will have much control over whatever device you have. How could they program your stereo to work with a multitude of USB devices?
I hate to be the pessimist here, I just see people getting their hopes up and it will suck when they're dashed.
I would love it if the USB interfaced worked with something like a USB hard drive and you could search folders. But the stereo would have to work with Fat32 or NTFS and it would need some form of playlist management.
More likely is the'll have a USB connection but you'll have to control your music from the actual device.
Still, it might be a better option if it's way cheaper than the ipod interface. I have an ipod and there's no way I'd spend $400 plus to buy the ipod interface and have it installed. Just not worth the money.