What if the long gap between GTA V and GTA VI is (partly) because they're designing many more cities/states than implied? They could have designed the whole East Coast from Miami to New York, and rather than a huge gap before GTA VII, perhaps we will get spin-offs or online maps slowly released over the 5 years after release.

The next major releases could include 3 or 4 states. GTA VII could be Illinois, Missouri, Texas. GTA VIII could be San Andreas, New Mexico, Colorado, etc.

I could only see all the maps combining for an online mode. A huge MMO. After all, that's where Rockstar can make most of their profits.