Other than generating buzz when the Stinger was introduced, Kia doesn't seem to be trying very hard to sell it - and that early press coverage was for enthusiasts and trade press, not average car buyers. The Stinger is not even in any Kia ads since the super bowl TV ad, at least not that I've seen.
As to the future - Kia/Hyundai didn't hire Peter Schreyer and Albert Biermann to build only a couple of cars.
Remember when you bought a TV from Zenith, RCA, JVC, Mitsubishi, etc? Now that market is dominated by Samsung and LG. Same for house appliances, with GE, Sears, and others gone or losing massive market share again to the South Koreans. Could the same thing happen with cars? I believe it could, but Kia and Hyundai have a lot of work to do to get there.