I think the Warcraft RTS community would go crazy if Blizzard were to actually release a good amount of NEW content for players, even if it were only bigger maps, that possibly have a new terrain. Let us run around in the Sahara Dessert or on a map with islands. One thing which already should have been done, make it so we can select ALL of our units at the same time, rather than only 12 at a time (or whatever the current limit is). I’d gladly pay for a QUALITY expansion.
If you announced this later this year, next year you could announce Warcraft 4 RTS, and then release it on the 20 year anniversary of Warcraft 3 Classic.