It would be cool if completely removing a tattoo required a doctor to do some work, maybe with a timer. The new tattoo system would support that well.
First time a doctor does it, the short-desc becomes
'%N has a faded tattoo on %p %bodypart.'
And the long description stays the same.
Second time, it blanks entirely.
I wouldn't remove SkinWriters' ability to alter existing tattoos to correct typos or do coverups. I might put in something like a 'help tattoo-play' to say that coverup tattoos should respect the fact that they are coverups, but let people handle that ICly. If you want to turn your dick tattoo into a flower and it makes IC sense, great.