My response when I read that post this morning (thanks to following Izzy on Twitter) was....

I think there will be billions of credit/IOU issuers - within suitable 'framework of trust' agreements - whose credit is based upon their capacity to provide goods and services.

But this people-based credit does not mean exactly mean each issuer creating a separate currency. What is needed is a unit of account by reference to which such exchanges are priced, and a framework within which these people-based credit units may be cleared and settled.

At the moment we use completely abstract (base-less/worthless) units such as £, € or $. In my view we will exchange our credit/IOUs by reference to a unit of energy.

And we will not just exchange our 'money's worth' units of credit for each other's units of credit, but will also be able to exchange them for units redeemable in payment for different types of energy, and above all for units redeemable in payment for property rentals.

A standard unit of account is not the same thing as a unit of currency. One can no more run out of units of account than one can run out of metres or kilogrammes. But one can certainly run out of currency/IOUs based upon finite resources.