Precisely. And it's important to note that distinction between Paradise Isle and Atlantis and say, Thor's Asgard. Asgard is truly separate from the world of "mortals''. Atlantis and Themyscria may be separate, but they are a part of the DCCU Earth. I think, intelligently done, you could explore all sorts of interesting ideas with that as a base.
Totally cuckoo idea (in other words, not one I'd specifically want to see on screen but a sort of thought experiment I had):
I remember reading when Kevin Smith was writing Green Arrow that GA had a team up with Aquaman and AM was disrupting a drug operation by Black Manta. GA says something about how he doesn't even understand how "You can even snort this stuff (cocaine) under water?" It got me to thinking... Lets say that you start having contact with the Atlanteans, diplomacy, trade, the whole nine yards. What if the Atlanteans, people whose biology is different from normal baseline humans, find out that eating certain kinds of surface foods, foods rich in certain vitamins that they just don't have a lot of being that the Ocean bottom ecology is different from the surface, that these newly imported foods actually act in there systems like a highly addictive drug. An Atlantean drinks carrot juice or eats a carrot and they are high as a kite say. How does this affect things? Do they become the biggest importer of carrots in the world? Do they bring their riches of the deep, gold, precious minerals that no one else can get to, to the surface, just for another fix? Does Arthur allow them to consume these foods? Does he outlaw them? If so... Well we know what happens with prohibition on the surface world. Does Atlantis have to learn this as well?
Okay, forget about the goofy food as drug idea. What about something a little more concrete? We know that Atlantis, while still being advanced has different classes. They have Royals and elites, and a fair number of plebian types. The Atlanteans now have diplomatic relations with various important and powerful surface world nations. Some captain of industry type hears about the inherent abilities of the Atlanteans. Their strength, their ability to survive great depths, their knowledge of the Ocean floor... He thinks... "These people would be incredibly suited to either mining or oil rig operations." Sure, the Atlantean elites might balk, and there would be even poor Atlanteans that might not want to be part and parcel of the surface world's environmental degradation of the planet... But there would also reasonably be those that would say, "Screw it... I need to eat. I want to make money. Here's an opportunity. I'm taking it since I aint getting anywhere in Atlantis' society any time soon." What happens then? How does that affect the wider world? How does this cause conflict? Cause I could see many ways it could. How does easy, or at least easier to bring to market gold affect the world economy? Would there be the forces of other wealthy interests that would be against a businessman having such an edge? Could that stir them to illegal action that Aquaman would find himself working against, even though it would mean helping those who contribute to the forces of environmental damage?
I think the surface has barely been scratched when dealing with the notion of places like Atlantis or Gorilla City or Paradise Isle being real, known places in the world. There is great potential stories of all kind if writers care to put some thought into it.