I was just looking for something like this too, We have a ton of amazing characters, and would like to have them all just have a basic idle loop, I certainly value the time of an animator making these come to life and have unique nuances, but in terms of economical and time efficiency, it would be amazing to have a service like https://www.mixamo.com/ where we would import and output the most basic of a character idle for common humanoid file conventions , Head, torso, RArm, LArm, etc..
Will explore the physics, maybe there is something there for now, that satisfies this ask