I believe this is possible, but you still need modern smartphone with NFC, and TrustedZone technology.
Being said that I think Microsoft, and PBoC, hold patents for offline transfers of digital currencies over NFC.
Idea is that you can transfer currency offline and when you have Internet connection you upload new state to miners.
This feature is very important to like half of the world today, who don't have Internet connection.

Is this possible to implement with bitcoin?

Some ideas:

- bitcoin would be transfered off the grid using only smartphone and NFC
- trusted execution environment technology could be used

This would solve some issues if it is possible. Such as trading in no Internet environment, like is the case in half of the world.

What's your thought?