Well what do you expect? Nintendo made Pikmin, so if there's going to be any others not related to the advance wars franchise (which wouldn't be a bad idea really), then you'll have to wait for third party. If third party aren't making RTS games for other systems, they're sure as hell not going to make them for Wii U. They absolutely should, but they won't. So that just leaves indies.
Speaking of indie Wii U RTS games....
Here's one, and it's a party RTS:
https://www.kickstarter.com/projects/prismaticgames/hex-heroes
And here's another one, and RTS-roguelike game, also for 3DS:
http://nintendoenthusiast.com/article/onipunks-c-wars-3ds/
And here's a sidescrolling RTS, and the first game is on the Wii U as well:
http://www.swordsandsoldiers2.com/
None of those are quite the straight RTS you're looking for, but still, there are RTS games on or coming to Wii U.







