I would really like to have a hardwired motion sensor. I have created one with an off the shelf module and the GPIO on my RPi and it works ok. However, it would be nice to have the motion sensor more integrated. Now that it's set up, I don't know if I would change that installation. However, I also have some outdoor lights elsewhere that are controlled by MS16A modules. They always seem to fail or have the battery die or <insert stupid issue here>. I would really like to install a set of hardwired sensors in their place.
If X10 made the PR511 sensors available on their own, I think I'm not the only one who would snap a set of them up (assuming the cost wasn't astronomical compared to other offerings). I see that as one module X10 dropped the ball on big time!
And while I'm at it, if they were to make them so you could local control via a WS467 (or similar) AND control the light (like the PR511) that would be AWESOME! If they could send the command to other lights, that would be even better. That would make it possible to control multiple outdoor light circuits from a single motion sensor (or link motion events on different sensors).