Instead of regular centralize stablecoins, why we don't have a stablecoin with its own blockchain or a token where anyone can mint or redeem that stablecoin using ONLY Cryptocurrencies at the market price.
For example if I have 1 Eth and want to mint it into Xusd (community stablecoin) it goes like this example:
If Eth market price = $1000 I send 1 Eth to this blockchain or contract and I receive 1000 Xusd.
And it can be redeem for any Crypto at market price,
If Eth price = $2000 I send 1000 Xusd and get 0.5 Eth.
What you are proposing seems to me very similar to what has already been implemented. These are wrapped tokens that are tied to the cryptocurrency for which they were issued. For bitcoin there is Wrapped BTC (WBTC), for ETH there is Wrapped ETH (WETH). They have pretty much the same price as BTC and ETH and follow their price all the time. And they can be exchanged for any other cryptocurrency. I may be wrong.
You do make a valid point, although wrapped tokens are more like a way to use a particular cryptocurrency on other Blockchains, but they pretty much don't allow you to use smart contracts or other decentralized applications.