DEX are already quite good for crypto-crypto exchanges. But they continue with the problem that the issue to trade fiat to Bitcoin has not been fully solved. It is still more risky to use them to buy or sell Bitcoin than a CEX:
I don't know if this is fully solvable, or if there have been new ideas to solve these issues in the last years.
I doubt that there is an easy way to solve this issue and the reason for that is simple, DEXes cannot operate with fiat money. CEXes have limited support for operations with fiat because they can receive and send wire transfers (SWIFT, IBAN, etc) in an automated or semi-automated matter. CEXes comply w
DEXes on the other hand have no way of integration with the fiat system because no bank or government would ever do that willingly, at least not in the near future. And since DEXes they cannot send or receive fiat money, they cannot really do any conversion between crypto and fiat.
IMHO the best that a DEX could do in that respect is to provide a distributed version of LocalBitcoins/LocalCoinSwap/etc. That is it would allow users to communicate and choose a way of transferring fiat (f2f, wire transfer, cash by mail, etc.). The DEX would also provide an optional escrow service and some kind of reputation score for the users. The reputation would be updated by the users after doing a crypto <-> fiat trade.
So that is pretty much all I can think of with regard to crypto <-> fiat exchange. Actually I think that if someone develops a DEX that supports all these features plus all the features of existing DEXes, including the ability to make atomic crypto <-> crypto swaps, that would be a great system.