BMW is set to follow the i3 with the i8, a plug-in hybrid sports car running on a 131-horsepower electric motor, a lithium-ion battery pack, and a 220-horsepower, 1.5-liter turbocharged three-cylinder engine. In the city, the i8 should be good for up to 20 miles of all-electric driving. On the highway, with both powertrains working together, the i8 should dart from 0 to 60 mph in less than five seconds, with an electronically limited top speed of 155 mph. Such performance won't come cheap: The i8 could cost $160,000. But if that's too rich, or the i3 is too small, potential buyers should wait a few years. A new sub-brand, BMW i, will produce the i8 and the i3. That's a clear sign that after years of testing the waters, more plug-in BMWs are on the way.