This is a nice strategy. You might need to use your fiat anytime in case when the ATM is not working. A complete reliance on the technology is not a wise thought and the mind set need to be changed a bit. Besides, the more cash you hold, the more you will be able to make instant transaction.

Investment in an asset with highest liquidity is also a ready source of cash as you can exchange it in the market anytime. So the importance of fiat cannot be ignored. However it is also desired to invest in assets for long term to get your investment replicated to save for future.