Sounds too good indeed!! That is a brilliant cool Idea!! 
Coming back to the cold reality, though, we would face 2 main issues:
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Skin is too “conductive” for it to work without some tweaks (yep, already mentioned, so will skip)
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Tattooing is a different process of printing:
When we print something, we deposit layers of ink on top of each other on a 2D plane. This helps make sure that the end result is a continuous line, so it can be used as a conductive line.
Now Tattooing is slightly different. What we see in the end is almost an optic illusion.
Instead of depositing ink in a 2D linear way, when we tattoo we end up with a loose 3D arrangement.
We deposit each microscopic droplet of ink at a “random Z-Axis” value, so even if we discard skin’s conductivity, the connection between the particles of in generated on a 2D printing process would be lost on a tattooing process. 
Yet I do love your Idea! and maybe there is a way to circumvent both of the above issues! (+ plasticity), especially since they are intertwined to some degree.
Problem there is that once you stick an NFC tag onto human skin… it just doesn’t work anymore. 
Similar thing as when you stick it on metal.
Too conductive a surface causing “interference” 
So you would need to address it in a similar way as metal-sticking NFC tags: an insulation layer in between!
Yet, then you’ll have a bumping sticker, which won’t last on someone’s skin for more than 15 minutes (especially in events where it will be accidentally scrapped off) 