This seems like it's easy to workaround by not modifying the existing trait but by defining a new trait with your new method, and impl'ing it atop the old trait

This seems like it's easy to workaround by not modifying the existing trait but by defining a new trait with your new method, and impl'ing it atop the old trait. That seems like a pretty ok 90% solution, and in a lot of ways cleaner and more well defined a way to grow your types anyhow.