Elite: Dangerous Steam keys will be given to Kickstarter backers as well as anyone who has purchased the game via the official Frontier store. The Steam version arrived in April, months after the game launched, and Frontier Developments had only said on the official FAQ that they were "investigating the possibility" of giving keys to players who wanted it in their Steam library.
The announcement states that owners of the game will be able to generate their own Steam key from their account page from May 28th. This includes any new customers who buy from the official store in the future. Frontier promises a seamless transition to the Steam version. Since all your save data is kept on Elite: Dangerous’ servers, it's simply a case of logging in with the same account and it'll be just like playing the non-Steam version. Almost as if it was a complete waste of time. Almost.
The latest Elite: Dangerous newsletter also mentions the imminent release of the Mac version of the game, which launches on May 12th. If you already own the PC version, you’ll get instant access to the Mac version for absolutely nothing. Commendable work by Frontier on both fronts. The more ways to play the game, the better.