It wouldn't be the Watch alone pushing the need for Bluetooth, the iPhone users want it too, Watch or no Watch.
I'd get it, and use it for both. Actually, I'd pair it with the iPhone, stream the music from the iPhone, but control it from the Watch.
Personally, I rather not go for long jogs or hikes around the lake without a way to make an emergency call, so I'll be carrying my iPhone no matter what (in my CamelBak).
People have had mixed results with Bluetooth, especially with sound quality, so I suspect Apple may have avoided it for that reason, but now with Beats, and with most iPhones now having the improved Bluetooth each, Apple may be ready to launch - and the Watch would provide good timing - but it's certainly not limited to the Watch. I'd be using it for all my devices.
I have a feeling I'll be getting the Jaybird Bluebud X though. They are really good. They are sweat proof, super light, stay in the ears, comfy, strong pairing, perfect - with a price to match - $125. Ouch, but I rather that then get crap for $70.