It's an interesting subject. I would really appreciate some feedback on the above stated inquiry. Thank you.
IMHO it makes no sense for the NFC tag to do the work, but rather let the wallet software on the smartphone do the work. As in:
- read NFC data (encrypted privated key)
- ask user for password
- decrypt
- ask if to import into wallet (warn about potentional dangers) or wipe to wallet via TX
- etc. pp.
Edit: which would very similar to the existing QR Code scanning methods and would most likely require very little code changes for e.g. Mycelium.