with bitcoin participants trying to come up with a pocket-able version, there can be enough supply in that form to meet that need while most of it is still decentralized enough to keep the confidence in the currency up.
It seems like a certified, pocket version could exist. You'd have to be confident the issuers were good for it, just like with any check or property certificate. Whatever level of decentralizing the supply among multiple issuers is needed could be achieved, too. I'd worry about counterfeiting, but how much more or less than with other attempts at a competing currency?
There's also the argument that bitcoin is too vulnerable to a collapse in computing. True, but the current stock market was responsive to a single Twitter account getting hacked. We all would be better off having something worth trading to cover a scenario of collapse where even de-centralized computing fails. It's not Federal Reserve notes or bitcoin.