I installed it on my 4s running 6.1. I'm guessing I could because I had paid for it while I was still running 5. Unfortunately I had to uninstall it. It broke Siri. Can't wait for an update.
Really hope they are working on this. It's the main reason I JailBroke my phone(slight exaggeration). Linking Siri to Waze and hopefully Google Maps!! That would be huge. I still have and use spotify premium just cause it was so awesome to have with AssistantLove on my iPhone 4. Miss having the world at my finger tip.