Here are some free ideas for Android and phones in general.

• The palm sweat meter (prove that holding hands just isn’t that bad, the scientific way). Should be doable using the humidity sensor in the new Galaxy S4.
• A game that simulates real physics. It will be dull but someone should make it just so it’s been done.
• Someone should properly figure out all the mDNIe fields so Samsung’s oversaturated OLED travesty can be somewhat improved. I did figure out most of them on the Galaxy S2 but lacked a colorimeter at the time so I couldn’t write a simple display calibrator. It is possible to mostly fix color temperature and gamma (same curve shared for all RGB). 10K+ color temperature makes me blue.
• An IR diod/front camera, so the useless Samsung face stay and rotate features can work when it’s not perfect lighting conditions. Like in bed.
• Or to take the previous one even further. IR camera+laser projected IR pattern. Then we could have kinect style 3D scanning in our phone. Don’t think I’m crazy, if you can stick a projector into a phone this can be done too.
• Bonus hardware feature: breathalyzer in next gen phones.

As you may have guessed I’ve used Samsung phones the past year.