The Court of Justice of the European Union has ruled against publishers preventing you from reselling your digitally acquired software within the EU.
Eurogamer has provided a link to the official ruling, suffice to say the ruling focuses on computer programs in general and does not specifically mention games. With that said, PC games are technically computer programs, making the ruling potentially impactful on services like Steam and Origin.
The ruling is an application of the principle of exhaustion to computer licensing, meaning that a publisher’s hold over a license is exhausted after the first sale. The new holder can therefore resell their version of the license to someone else granted they make their version of the program “unusable at the time of sale.”
The theory is just and sound, but the reality of its implementation seems unrealistic in the realm of digital downloads, especially on PCs where it is easy to manipulate folders and files pertaining to licensing agreements. We will have to wait and see how this impacts digital download services for games, if it does at all.