Well, I tried doing some reverse engineering with storage issue. It seems they have dedicated around 7GB for Operating System itself, and it was full (very little space left). People are making noise over TW bloats, but TouchWiz framework and apps are not taking MUCH space here. What Samsung probably can do here is
1. Optimize all the xxhdpi assets (as @
dafreaking said), yes xxhdpi takes a lot of space. They should probably optimize and reduce size. I did some PoC on how much memory XXHDPI requires. Well, the total size of an app SecSettings.apk is around 94mb. XXHDPI images (most of them are duplicated in different layout assets) occupy 35mb. That means, around 40% size of an app is consumed by XXHDPI images. So practically if Samsung can remove duplicates and optimize, they can save 20%-25% of space.
2. Remove all the third party applications (and there are some GAMES in /system/apps too.. I don't know why Samsung developers put games in it)
3. Remove unused libraries. SGS4 has many unused libraries laying in system dump.
4. Restructure partition and add the obtained free space to internal storage (/storage/emulated/0)
If done correctly, we can get 1.5-2GB extra. If no Samsung, someone from us (XDA) would have done it because it is needed. One more thing, We should force Google to reactivate feature "Move apps to SD Card". Being on Android means to give more control to user and I don't think Android is going on that path :-(