Yes, since in theory, following semantic versioning, there should be no BC breaks until the next major version, it seems like it should be safe to pin it to ~2.3. I see @Ocramius 's point regarding potential for unintended consequences with minor releases, however, that will also mean more administrivia for minor releases, as every package would need to have it's composer manifest updated sooner (assuming there is a 2.4 before 3.0).