Elite: Dangerous has made an intrepid journey across multiple star systems, and now finds itself in the orbit of Gaben Major. In other words, Elite: Dangerous can now be purchased through Steam.
To answer the obvious question first; Frontier does not currently have plans to give existing (non-Steam) owners of the game a Steam key. They also haven’t ruled it out. Producer Michael Brookes says “We haven’t removed any option – as for providing steam keys for people who already own the game we’ll look into it and go from there.”
You can, of course, still add Elite: Dangerous to Steam via the “Add a non-Steam to my library” option. But that’s not really the same thing.
The Steam version of Elite: Dangerous does not (at present) have Steam trading cards or achievements or anything like that. It’ll be possible to update the game through Steam (just as people do at present through the launcher,) but any DLC will still need to be purchased through the Elite web store for the moment.
Still, it only just arrived on Steam today. Frontier may have plans to experiment with further platform functionality in the future.