I don't see the point. I can mute with my tuner or my amp. The less electronics in my bass the less there is to go wrong.
Sure you can find reasons for one. I can find reasons not to have one. The pedal tuners on the market are far more accurate than the headstock variety, especially for bass. I don't want an on/off on the guitar for the same reason I don't want one on the mic. More things to go wrong.
+1... if I really wanted one, it wouldn't be a big deal in install one - it's really not in issue for me, though...
- georgestrings