One idea I had for the Isle of Opposition, for my adventure that I really might propose some day, is that characteristics of the portal destinations leak out a little bit onto the Isle. Primarily this manifests in terms of climate and terrain, though it could be other things as well. I imagined that the KoJ gate opened onto a cold, possibly snowy and mountainous region, so there is a cold zone around that gate, while the VoB gate opened into a steamy lowland jungle, so there is a hot humid zone around that gate.
Furthermore, whatever mysterious force or forces established the gates also tends to keep the area close to the gates "morphically locked", if you will. So that if you tried to build a fortress around the gate, for example, you'd have a hard time, with the walls constantly cracking and crumbling and the foundations sinking into the ground. Within a matter of months the fort would lie in ruins as the original shape of the land reasserts itself. This is not a matter of pure theory: the dragonborn from the KoJ tried building several forts on top of the portal, with no success. Eventually they gave up on that project and instead established an armed and fortified camp about a mile down the road.
This characteristic of the gate area also explains why the main port and trading area is in the center of the island. Some have tried cutting steps or building scaffolding into cliffs at the mouth of the harbor for direct access to the gates from the water, but these fall apart almost immediately. So goods and people coming and going from Daunton have to be landed at the midpoint of the Isle and then travel overland to get to the gates. Similarly, to get from one gate to the other you have to travel overland around almost the full circumference of the Isle. (Look at the map of the Isle with its crescent shaped harbor, and gates on the horns of the crescent, to see what I mean... the gates are pretty close to each other as the crow flies, but as a practical matter they are far apart!)
Of course all this is just stuff I had as backround for my adventure and has never actually appeared "officially", so feel free to ignore... but feel free to use if you like it.