Form my understanding, the U-bar is not going to be available separately. It is part of the
signature guitar, and will only be available for that guitar.
Having played the guitar, I can attest that the U-bar gets in the way of any traditional palm muting. The stem on the bass side runs parallel to the low B saddle. It won't get in the way if you mute above the
bridge pickup.
Cheers,
Butch