Same here - my iPad 3 was used by me and then 2 children growing up. It's still working perfectly fine and has even decent battery life. But the app store shows a blank page, and even if it wasn't, all recent apps have a higher minimum iOS version (edit: because recent versions of Xcode will only build against recent iOS versions). And Apple is actively removing apps from the app store that haven't been updated in a while. So the hardware is still fine, but there is no software available anymore and no way to sideload.