Privacy coins are getting delisted from some centralized exchanges but I do feel that the best place for privacy coins is DEX exchanges because of their anonymous use cases, also I think that privacy coins represents the real decentralization than other projects trying to claim decentralized..
The problem with this is that most current DEXes support on chain transactions not cross chain and even if they allow you to trade coins from different chain they achieve that by wrapping coins in centralized way.
This is the sad reality about DEX right now. It very hard to do cross chain on multiple blockchain unless they do the method like what you said. So far I only see maximum 2 blockchain cross chain so far and combining all this privacy coin is really a big challenge to the developer. I'm not familiar that much to the principle of atomic swap but I heard that it might be a solution for cross chain issue.
You maybe missed some older projects that already had a lot of functionality before ethereum even had a GUI wallet!
I mean there were project back in 2015 (
NXT,
NEM,
QORA)
that had features like a decentralized asset exchange, blog, chat, naming system (DNS),
address alias system, build in multi signature accounts, polls (voting) and
cross chain atomic swaps.
It seems whenever some "new" already existing feature is launched on ethereum
all the news are reporting like a big achievement event if this stuff existed 4 years before on other blockchains.
Unfortunately NXT fell into oblivion even if it had the 1st decentralized asset exchange.
Maybe it will be rediscovered again!
Regarding cross chain atomic swaps, QORA was the first blockchain that implemented that feature.
It was possible to trade QORA with BURST without 3rd party and middleman directly on chain.
At that time QORA technology was ahead of time but is seems nobody cared about it so it fell into oblivion too.
Now there is one new community project in ongoing development named
QORTAL which is based on QORA but with new code. It will be soon possible to trade QORT/LTC pair
using cross chain atomic swaps without 3rd parties and no middleman involved!
Remember people the golder rule: Not your keys not your crypto!
I invite you to check the QORTAL thread here
https://bitcointalk.org/index.php?topic=5258519.0if you are interested in using the platform in near future
or if you would like to support or help developing the project.