I totally support any kind of map expansion, but I believe small islands would be more viable for a non-paid DLC. Considering SA is a big isle, it would make sense to add more places surrounding it.
Every new DLC would feature a new place/city to explore. These cities would contain specific businesses according to their enviromnent, nature and resources. The new businesses would consist in exporting stuff to LS and Blaine County, requiring new vehicles and capabilities from the player.
If the island is place with nature and mountains, mining would be a good business considering LS is demanding gemstones or gold below market prices.
In case the new island is a congested city, smuggling would be there, but the hangar would be replaced with a marina as part of a Naval DLC. It would be called Piracy.
Talking about Naval DLC, it would make more sense because more people would roam between the islands and you wouldn't be navigating in circles.
- Mining and Piracy businesses available as part of the Naval DLC.
- The sea would receive a big update as well with oil-rigs, undersea places to explore, sunken ships, secrets and more.
- The yacht would receive its first update and could be related to the new Piracy business.
- The new islands would contain airports or airfields with new hangars available.
- The "nature" island would have mines and underground secrets to explore; hunting animals would be possible. Police wouldn't bother you there, unless you kill a local NPC, call it or "bring it" with you.
- Ability to export cars, drugs and other stuff to the new island with a higher risk.
- New vehicles, submersibles and more...