This response came straight from Dovetail on their steam hub:
There seems to be a bit of confusion here. Hopefully this will clear the situation up.
Dovetail Games has acquired the rights to distribute the multi-award winning Microsoft Flight Simulator X: Gold Edition via Valve's popular digital retail channel, Steam, entitles Microsoft Flight Simulator X: Steam Edition. Box distribution remains in control of Microsoft and is unrelated to the announcement we have made. We will be acting as a publisher for Microsoft in relation to FSX. We have a license to re=release FSX on Steam and this does not extend to making product improvements. Ultimately overall direction for the product remains with Microsoft.
As stated we have also acquired a global licensing deal with Microsoft, granting us the rights to develop and publish all-new flight products based on Microsoft's genre-defining flight technology. We are currently investigating new concepts in this area and is expecting to bring a release to market in 2015
- Martin