As of today a feature and breaking change freeze is in effect for the first official alpha of MODX 3.0. This means that until the alpha1 release is made available, only bug fixes and lexicon updates will be accepted on the 3.x branch on GitHub.
Just to clarify, new features and other breaking changes will be accepted again after the alpha1 version is available. The actual 3.0 feature/breaking change freeze wont be until we reach the beta stage, and we're not quite there yet.
The goal for this temporary freeze is to make sure we don't accidentally break the alpha1 build, with a new exciting feature built by someone a day before that happens to contain a bug. We still want to see that amazing feature, but also want to make sure there's time for testing it in development and with nightly releases, and there simply isn't such time for alpha1.
The milestones have been updated on GitHub for any outstanding pull requests, indicating it they are still suitable for inclusion in alpha1 or not, and the integrators will be working on the final stretch very shortly.
If you'd like to help with preparing for alpha1, consider helping with the 3.0 documentation, testing the latest nightly build, or checking out what's left to review/update for alpha1 on GitHub.