I haven't noticed anything on the mailing lists for quite a while. I remember around the 22nd of last month I tested the switch and it worked, but I didn't have time to check and see if it did anything other than not say 'unrecognized command'. So does replaygain now work in lame? If so is it implemented in alpha13?

Lossy

Just encode something with current 3.94 alphas. You will see a replay gain value at the end of encoding. You do not need any switch for this.

A parameter is only need for clipping detection.