Well, from what whylightbulb said on WDWMagic, the 3rd gate is roughly 10-15 yrs away. Right now, they're doing as you just said - making both parks full-day affairs (adding rather than replacing, maximizing space such as the new Springfield area and Transformers, adding more attractions than what was there before like Diagon Alley has, more than likely planning to fix other dead areas/bottlenecks - KidZone, front of Toon Lagoon, etc)