I've seen a blog post from an Intellectual Property lawyer who specializes in video and board games being passed around my social media circles recently, and I think that it is something that needs to be looked at.
Keep in mind that I am not a lawyer, so don't take anything that I talk about as any sort of legal advice. Find someone who specializes in intellectual property law and get their two cents first.
The way that copyright and game rules intersected in the past was basically along these lines: you can copyright the exact expression of the rules, but not the underlying ideas of the rules. If you re-expressed the rules with your own wording, you were free of infringement. There were a few restrictions on that, like saying that mathematical expressions used to determine parts of your rules could be copyrighted, which lead people to finding new math that was close enough to the old math for government work.
This is what lead us to games like Mongoose's version of the Runequest game, and large swaths of Old School Renaissance clones of early editions of Dungeons & Dragons.
The case that looks to have changed this was between two board games, one of which effectively cloned parts of the mechanics of the other game (you can find more detail at the link in the first paragraph, I'll let the expert do the real explaining of this issue). The first game's publisher sued the second game's publisher for infringement and eventually won.
According to Zachary Strebeck, the lawyer who originally blogged about this, the suing publisher's case was based on an earlier precedence that "the plot and gameplay progression of something like The Legend of Zelda would most likely be protectable." However the court did not feel that the allegedly infringing game fit that definition.
The court points out that “Unlike a book or movie plot, the rules and procedures, including the winning conditions, that make up a card-game system of play do not themselves produce the artistic or literary content that is the hallmark of protectable expression.” They note that past game copyright victories were won by parties based on infringement of visual appearance or other protectable elements. Pac-man’s gameplay, they recall, was not considered protectable back in 1982.
Given these rules and precedent, the court looked at the issue in the case – that of the similarity between “the roles and characters and their interactions” in the two games. Ziko argued that these roles and interactions were no different than other rules and mechanics in the game, and therefore were unprotectable. DaVinci, on the other hand, argued that those roles and interactions were protected, using precedent from the Triple Town case.
The court distinguished this case from the Triple Town case, though. In Triple Town, that court analogized the gameplay hierarchy in Triple Town to the plot of a movie. In doing so, they imbued it with copyright protection.The "Triple Town Case" refers to a 2012 case between EA and Zynga overly game apps Triple Town and Yeti Town. One of the stipulations in that case made by the court was that "the object hierarchy coupled with the depiction of the field of play comprise a setting and theme that is similar to Triple Town’s. A snowfield is not so different from a meadow, bears and yetis are both wild creatures, and the construction of a 'plain' is not plausibly similar to the construction of a 'patch.'"
Where things get interesting for the cloning communities in tabletop RPGs is in this analysis of the case:
The assessment of each game’s UI gets to the heart of the EA-Zynga dispute. Like Yeti Town, Zynga allegedly copied the basic gameplay from EA and then put its own lightly modified UI elements on top of that gameplay. Indeed, as alleged by EA, Zynga probably did less to modify its UI than Yeti Town did. The Triple Town ruling suggests that Zynga probably can’t score a quick win.The two ended up settling because a precedence setting win would have ended up having long term ramifications in a business where "borrowing" from other games is such a fundamental part of game design.
Like I said at the beginning, I'm not a lawyer and I'm not going to attempt to try to explain this complicated material. I suggest looking at the information and thinking what would happen if there were a change of the people in power at Wizards of the Coast, and they decided that they didn't like the cloning of their systems.
Material used directly from the OGLs would still be usable, but what about the "extrapolations" to make the OGL material play more like older systems? What about designers who make "diceless" RPGs by re-expressing the old rules with their new language? In what ways could the assumptions of copyright law change for them dramatically?