D&D's new rules will be available under a Creative Commons licence
Once all three revised rulebooks are out.
Last year the Dungeons & Dragons community imploded over a leaked draft of a licence change that suggested Wizards of the Coast was planning to restrict how the D&D rules could be used by anyone publishing third-party supplements, or separate games derived from D&D's 5th edition ruleset. At the peak of the outrage, Wizards of the Coast fully retreated from the proposed changes, and promised to make the base rules available under a Creative Commons licence.
In January, Wizards lived up to that by putting version 5.1 of the Systems Reference Document into the Creative Commons. However, since revised versions of all three core rulebooks are on their way, with the Player's Handbook due in September, the Dungeon Master's Guide in November, and the Monster Manual in February of next year, the question remained: what would happen with future updates to the rules?
Wizards has now announced that "within weeks" of the revised Monster Manual's publication, the SRD will be updated to version 5.2 and also released under a Creative Commons licence. "It’s a massive update!" the FAQ promises. "SRD 5.2 will provide revised rules at the same scope as 5.1. Creators will have the tools they need to create content using the revised and expanded ruleset. It will not, however, include lore references."
So don't expect trademarked monsters like illithids or beholders to suddenly appear in the Creative Commons, but do expect a bunch of new rules additions to D&D's fifth edition (weapon properties, maybe?) to make the leap.
Calling it a "massive update" is promising, but Wizards has been stingy with the SRD before. Version 5.1 only includes one feat, for instance, the not exactly world-shattering Grappler, and only one subclass for each class. That's why a game like Solasta: Crown of the Magister has to invent new feats and subclasses so you're not stuck playing the boring old fighter subclass of champion, which is the only one currently in the SRD. Fingers crossed version 5.2 is more generous with the revised rules' additions.