In order to do the Steam release justice, we have some infrastructure work remaining to do that will take more time. Our new release estimate therefore is sometime later this quarter. We will keep you updated on our progress.
The net positive of this is that we can ensure the release is more polished and that it will meet the user expectations of your average Steam user.
RetroArch 1.7.8 however is going to be imminent within the next two weeks.