I'm working my way down the thread post by post.
Some promises have value, while others do not. Which are which will vary over time. The same is true of other commodities, although promises are typically more volatile. Gold certificates have been successfully used as a long-term store of value and as an exchange medium for high-volume trade -- for suitable values of "long-term" and "high-volume".
If Monero was accepted as having similar characteristics to gold, would you see these promises manifesting outside of the blockchain, or as a part of it? I could send someone a certain amount of gold, or I could issue a promise that their gold (ex: Monero) will be ready to be placed in their hands on demand. I've imagined an infrastructure, like banking, that can be built on top of Monero .. specifically utilizing the tx_extra field (or perhaps not, as it may be better utilized in things like recurring monthly payments). I'm unaware of how this could come together, or if "banking" is even the correct word for what I'm trying to describe. Your mentioning of certificate issuance indicates, to me, that you are of a similar opinion.
Physical metals have persisted in storing value longer than anything else, and were used for essentially all trading worldwide for centuries. Arguably, some of the features of gold certificates which make them more usable for larger volumes of trade (in excess of say, a million dollars in value, pick a number, corresponding to the strength of your back) also contribute to their inferiority as a value store, relative to physical metal. That does not mean that they are not suitable for both uses, within their actual limitations. Gold or silver certificates which are fully backed by deposits and have the full faith and credit of their issuer are a pretty darn good value store.
I'm trying to define a word here. When you mention volume, are you referring to trading volume (# shares traded) or something else like the specific amount of value traded (not # of tx's) in a certain amount of time? In bold, which features of metals do you see, other than being fully backed by one's strength, lean toward high value transactions, while at the same time "contribute to their inferiority as a value store"? Could one be that they have functional uses other than a store of value (eg, electroplating)? Or something more economically related, the fact that they are capable of being more easily seized/become a target of seizure with an increased size of holding?