I can see that a lot of people will have their opinions on the direction of adding a DEX to Statemint.
Here is my two cents.
I talked about a scenario like this here: How XCM will actually be used with XCMP
As stated in that post, we know for sure that asking users to constantly move funds between parachains will be very inefficient and provide a really bad experience for users. I expect that there will trivial DEX pallets deployed to many chains, even those outside of the DeFi world.
If we agree that statemint will be a hub which contains many different tokens (both fungible and non-fungible), it of course makes sense for there to be some functionality allowing users to trustlessly trade between different assets.
I do not expect that a DEX on statemint would be competitive to any dedicated DEX parachain (in terms of liquidity, UI/UX, or feature set). Nor would I expect there to be any kind of profit mechanism in this DEX, which might have made it a competitor to other parachains. If parachains do feel some single minimal DEX pallet is a competitor, perhaps they should question whether their parachain is bringing enough value to the network.
I also think, if another Parachain can offer a service which completely overshadows the DEX on statemint, then that is great! In some ways, a really base level DEX acts as a floor to our ecosystem, and we should push parachains to provide experiences which incentivize users to trade on their chain, versus keeping assets on statemint.
Finally, I would probably want to point out that thanks to our governance systems, no decisions made now or later has to be permanent. It seems backwards to our philosophy to be afraid to add some feature. Instead we should welcome experimentation (of course prioritizing security and safety), and let users decide how they want to use products.
It seems obvious to me that the upside at this time far outweighs any speculative downside.