Every currency has a value theory. USD has military hegemony and financial market centralization. China has exports and foreign land holdings. CHF is backed by gold. The Euro is trying to become a regional 3rd world reserve through remittances. Labor-based currency has been tried, but, you probably don’t want to know about it.
Assuming all other aspects are solved.
The primary value of cryptocurrency is there not being a central authority to inflate away its value (through bailouts or economic 'stimulus').
Smart contracts offer the same fundamental value: you know what you are getting into and no one authority can change the terms on you.
With the SQL database, that would be quite easy. With actual bitcoin wallets (or the lightning network) essentially not doable.
[1] https://news.ycombinator.com/item?id=27628739
p.s. for people wondering what LN is, it is essentially:
Pairs of people agree to split some locked up bitcoin a certain way.
If they want to exchange bitcoin, they agree on a different split.
If someone tries to cheat, Hashed Time-locked contracts (the crypt magic that makes this work) means you get to take all of the locked up bitcoin".
The transactions can just be recorded in this SQL database, and the "reserve" would be untouched. If someone wants to exchange their BTC to USD or Euro, they can go to a money changer, their SQL database entry will be decreased, the money changer's SQL database entry will be incremented, and the total BTC in the reserve remains.
Hmm, I think I just described the so-called Lightning Network, which means in the end you have to trust a central authority after all. (EDIT: After reading about LN, it seems this isn't how the Lightning Network works).
They might as well make something like "El-Salvador-Coin" without needing dumb blockchain stuff.