It's a $20k, street-legal, EV modding platform. Sounds like you can mount your own infotainment system. Just an electric motor, battery, and chassis, and the rest is up to you. Isn't this what we've been asking for?
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If passengers want to DJ, you can get one of those little FM transmitter thingies that plugs into a phone/table headphone port.
edit to add: if Slate is successful, I wouldn't be surprised if a decently sized ecosystem pops up around easily installed custom sound systems and the tablets (possibly with headphone jacks!) to control them.