Eldin, if you look through the first page of this thread you'll see that I asked Dave about that very issue. Long story short: The GOG pre-order does not include a Steam key (though the physical pre-order does), but Dave offered to give me a Steam key after Resonance releases if I send him an email of my GOG receipt. I feel uncomfortable guaranteeing that Dave's promise to myself applies to everyone else, however (as that would be putting words in his mouth that he never said), and would suggest that you contact him personally via email to obtain your own assurance unless and until Dave makes a public post promising everyone the accomodation he was gracious enough to offer me. He is, after all, a very busy fellow and may or may not be concerned about getting swamped by people expecting post-release Steam keys.
hope that helps.
