The rumor on the Corvette Forum right now is that there is going to be a new version of Mobil 1 0w40 coming out which meets the Dexos specification and will be used as the factory fill starting with the 2019 Corvettes. It will also be backwards compatible on the Corvette too. It will most likely be a completely separate version of the current 0w40 which is formulated to meet a lot of European car specifications.
I'm undecided as to whether I will run this oil on my future 2018 Corvette or if I'll stick with 5w30.
Looking at the dexos1 and dexos2 tests at http://www.aftonchemical.com/Afton/media/PdfFiles/Specification_Handbook.pdf
it looks like the current 0w40 would pass all the dexos2 stuff except phosphorus, sulphated ash, and/or sulphur limits. If it falls under dexos1, it would need to pass the Fuel Economy Testing Sequence VIB, and a 40-weight HTHS 3.5 oil like that can't pass that test, even with a ton of moly FM thrown in like Pennz SRT 0w40 has. ...... I guess they have to amend the spec! GM can just shape the spec to suit their needs, since they are in the driver's seat here.