I have my doubts about decentralized exchanges because of them being so tied to centralized payment systems when it comes to fiat, but when it comes to cryptocurrencies, decentralized exchanges seem to be the future. So, services like Cryptopia will eventually become obsolete, because their main feature is listing of wide variety of altcoins.
Fiat can be replaced with USDT or any other stablecoin. Yes, it's not exactly decentralized, but you can freely move the stablecoins without asking for permission, and that 24/7, which makes it a great alternative.
I'm sure that a lot people are open to stablecoins considering how strong and superior the adoption of USDT is. It's the only coin/token that actually does what it is meant to do, which can't be said about any other crypto.
The volumes USDT generates are twice as much as its market cap, which is pretty insane if you think about it, and that after all the shit and fud they went through. It's here to stay, regardless of what people think of it.