Here's an idea: The moment the device is no longer supported, unlock the bootloader. If you really felt philanthropic, release some docs on the hardware interfaces. This way Linux / *BSD / Haiku / whatever could be ported and extend the usable life of the device. This would foster a thriving second hand market, massively reduce the security risks that users of the older devices are exposed to, help clear old stock, k…
Most developers are still going to be targeting iOS4+ for a while to come.