It was one of the highlights of the show for me, but I think once was enough. I wouldn't want to see them do it six more times, culminating in a walk-on cameo from the actual Miley Cyrus.
I think they could do it again. As much as like Cranston, his impersonation of Billy Ray wasn't exactly spot on. Any white male castmember or guest star in their 30s or 40s could easily fill in for him if the sketch is recurring.