Local bank apps. My carrier app. As well as a good MEME app.
And what do 90% of those have that their mobile website doesn't? And WP is big in the UK so contact those companies and point out that they're not supporting 1 in 10 customers.
A web browser with chrome cast and apple tv integration, a media player with chrome cast and apple tv integration (don't say AVcast cause that sucks), snapchat, and google hangouts.
Those are the apps I would like to see, but more so i would like to see first party app developers who actually care, and update at the same time as IOS and Android.
1. Lexicomp
2. Micrometer
3. More medical apps
4. Official Starbucks
5. Popular social games
6. Fully integrated Skype (shouldn't need an app for this, should just be baked into WP)
IFunny might keep you occupied till then...