Although we can't directly measure the one way speed, can't we at least demonstrate that the speed of light is the same for various arbitrary directions? I'm imagining sending a very brief & well columnated laser pulse aimed at e.g. Pluto, such that we have to "lead" the shot based on light travel time. If the outward bound light pulse travels slower/faster than expected, it will arrive at the wrong time & miss the planet, won't it?

You could repeat the experiment at different times of the Plutonian year to verify other directions, etc..

I think there may be practical problems with this method in terms of creating such a well columnated laser pulse, but in principle couldn't we use it to rule out anisotropic light speeds in several (perhaps most/all) directions?