I don't know if this is the right spot to put this, but I think a nice feature to have at some point is the ability to limit how many traits a player can select in the world editor.
That way the player can have a playthrough of the world more in line with the author's vision, before messing around in the editor if they want to be able to select all the traits.
I'm mean it sounds like you're completely onboard with the idea, whether it be mutual exclusivity for traits or a hard number of picking 3 out of 8 traits. I just want there to be the option if author has a specific vision for a 'vanilla' playthrough of their world. Meanwhile the player can enter the editor and disable the trait limits if they want to do so.
I don't see what's wrong with asking for that. I'm not asking to password protect or lock the editor, so that the players are stuck with the trait limits. It's more of a person waving a sign saying, "Please only pick two." Or "Please don't pick Futanari and Femboy at the same time."