Actually, I just had another idea. It may be just me, but I already have an Alexa echo, and Smart Home controlled lights and fan in the bathroom. All you really need is an WIFI-enabled motion sensor - and then, an easy way for it to start playing music on my alexa - bonus if it would automatically turn on the lights and fan when I enter, and turn fan of 15 minutes after I leave. Maybe even just an integration with IFTTT or Home Assistant.