If I stretch my imagination I can imagine a future where CBDC’s would use Bitcoin or Grin as Proof of reserve. But that would be up to a third party to implement. Basically it has little to do with Grin as project or the technology behind Grin since anyone could use it as a reserve and proof so by for example sharing the public keys of wallets holding the reserves.
I do not think Ignotis would care much for such an idea, but I do ofcourse not know his/her/their mind.
For the interested reader the closest thing i could find that represent an opinion or actually just a sharing of information on PoS by @igno.peverell: