I'm not sure how useful this is, but Valve has added the ability to remove a game from your Steam account through their customer support website. When you log into Steam with your web browser, or select “Steam Support” from the Steam Client's Help menu, you can select a game and see its available options. One is “I want to permanently remove this game from my account.”
I don't exactly know all of the specifics for will happen when you do this, but it sounds like you will need to repurchase the title if you change your mind. This is probably most useful for free little experiences, like Portal Story: Mel or Dr. Langeskov, The Tiger, and The Terribly Cursed Emerald: A Whirlwind Heist, which you've completed and don't want cluttering your Steam library.
On the other hand, users at NeoGAF, who (of course) broke this story, are concerned that it will be abused by trolls who phish accounts. Not only can they sell off their items, they can delete all of their games just because. I would hope that Valve has methods to track deleted games, even just for a limited time, in extreme cases.
On the other hand, a service like GoG could benefit from this feature. Since everything is DRM free, it could provide a transaction and let the user delete the record after they purchase it, rather than flaunt it on a public profile as Steam sort-of does. In that case, deleting the record wouldn't destroy the content — just place the burden on the user to back-up.