Hi @jamesbrown,
Sorry for not being clear on the meaning I put in the definition.
i was just following @steemrollin economic assumption that Bitcoin can serve as a store of value, medium of exchange and as a unit of account. I absolutely agree with you that Bitcoin at the limit will likely be turned into gold, i.e become the store of value.
What I meant by exchange of value should be considered in the vein of medium of exchange.
At the limit (one the last coin will be mined) I think this function will disappear as there will be no apparent incentive to mine and therefore maintain the network to fascinate exchange (as in I send you 1 Bitcoin out of my wallet to yours, but there could be none to validate the transfer).
And the solution to this problem (of preserving the network) would be an interesting experiment in itself.
Yeah, I read somewhere that miners will be paid in transaction fees alone at that point, but that's a major problem if bitcoin isn't spent at a high velocity and no one is going to want to use it if the fees get too high to offset the lack of minting rewards.