As far as I know, we’ve never had a developer/publisher pay any amount of money to generate keys on Steam, so unless this doesn’t kick in until you hit very high key amounts (100,000s - millions) I don’t believe this is a concern. You may be thinking of Sony and Microsoft, who (I believe) both charge money to generate keys on their respective platforms.
As for the idea itself, there are a lot of factors that I believe would make this a pretty complex task both from a business perspective and from a technical perspective. So far, I believe the best path moving forward is to continue to regularly release games, find a sweet spot in game cost inflation, and the big one, finding alternative reasons to spend coins besides just games.