Your are are hostage once Apple stops supporting your device, and it becomes officially impossible to install any software on it. Consider the case of a perfectly functioning iPad 4. If I wipe it and hand it to my nephew, there's nothing he can do with it. Nothing in the AppStore will install on it, and sideloading is impossible. Aside from chucking a perfectly working device into the e-waste, which I hate to do if someone else might get a year out of it, the only other options are complex, dubious hacks.