Automotive News spoke with anonymous sources at Porsche who said the car will probably be shown at the 2017 Geneva show. This would fall in line with a report that slated the wagon for a 2018 release, which would make sense to reveal the car in 2017. We've also seen a Panamera prototype with a lengthened roof testing at the Nurburgring, indicating that Porsche is working on one that could be close to production-ready. In addition, Porsche's North American CEO confirmed the US will get a Panamera wagon if it reaches production.
If it reaches production, the Panamera will be almost without competition in the US. While it would compete with the Mercedes-Benz CLS Shooting Brake, as Automotive News points out, and the Audi RS 6 Avant in Europe, the US really only has one midsize, luxury wagon left on the market it would face-off with. That would be the Mercedes-Benz E-Class wagon. The current generation is only available as the E400, but we expect an AMG E63 model to be official soon. While an impressive vehicle in and of itself, the E-Class still has traditional, upright wagon proportions instead of the sleek, raked shape of the possible Panamera wagon. The E400's 329-horsepower twin-turbo V6 is also a perfectly competent engine, but the standard Panamera packs a 440-horsepower V6, and it only gets more powerful as you move up to the hybrid with 462 and the V8 with 550. All are engines that would likely be available on the wagon.
UPDATE: A previous version of this story incorrectly stated that the E-Class wagon was rear wheel drive. It actually comes with all wheel drive standard. The text has been altered for accuracy.