You may not be buying or leasing a new car the next time you start thinking about getting a new ride. Instead, you may be getting a subscription that allows you to get whatever car you want, whenever you need it. In a bid to keep potential customers from defecting to ride-hailing services and foregoing personal car ownerships, brands like Volvo, Cadillac, and Porsche are upending the traditional retail model by developing app-based monthly subscriptions that provide vehicles on demand.