Hello,
I'm thinking about the following issue:
Paying cash at a POS should take only a few seconds. 
On the other hand, a Bitcoin transaction needs approximately 10 minutes to be confirmed.
To use Bitcoin in this situation, the confirmation of a  transactions should be just as fast.
Of course, this can not be done by the mining process.
But maybe some kind of a trusted confirmation service could help.

Are there any ideas?