How are ephemeral tattoos any different than today's temporary stick-on tattoos or (as a sibling comment points out below) henna designs? I'm not seeing how the art form or value will be impacted as tattoos would, for the most part, still be permanent for those that are serious about their ink.
It would be strange if the value of tattoos is in large part due to many people walking around with tats they don't want.
It's all about how temporary it is. A few days to a few weeks is definitely different then having something that sticks with you for at least a year.
I'm sure the designs will change, as will the motivations for getting them. Beyond that, this technology would be difficult to differentiate from a traditional tattoo whereas henna and temporary tattoos are visibly different.
It would be strange if the value of tattoos is in large part due to many people walking around with tats they don't want.