I don't know what's DAI, but there cannot be a really decentralized stablecoin in fiat, as it's against its nature. A stablecoin is pegged to another currency. If that currency isn't decentralized (such as bitcoin), then whatever manner you choose to maintain the 1:1 peg, yours isn't either. There can be a bitcoin stablecoin, with the use of cryptography, but there cannot be a fiat stablecoin, due to the lack of transparency.