The company has plenty of competition, such as Daimler's Car2Go and BMW's ReachNow. However, this is really part of a larger strategy rather than an attempt to knock down the incumbents. In a sense, Lime's strategy is similar to that for Uber and Lyft -- it wants to be a general-purpose mobility company that offers the vehicle you need, whether it's a scooter for a quick errand or a car for a lengthy shopping trip. If the Seattle service works well, it could become a staple in cities where Lime operates.

For Lime, the challenge is juggling this with its mainstay scooter business. It already has to deal with multiple recalls and hesitant cities. Car-sharing may only help if Lime's regular offerings are strong, and that's far from guaranteed. Lime's popularity in the scooter world can only translate so well to cars, too. While it'll have name recognition, it'll have to show that it can adapt to a significantly different field and compete with the best options.