What WhatsApp calls a difficult choice, withdrawing support for certain mobile platforms still in circulation is actually simple calculations, about the cost of maintaining the application VS the number of users who still connect using that platform.
According to recently updated information on the technical support page, WhatsApp will stop working on all Apple devices running Android version 4.0.4 or earlier. Those who use such phones will be prevented from re-logging into their WhatsApp account or creating a new account, with the app displaying the message "For the best experience, we recommend using the latest version of Android available for your phone." Except for the unlikely scenario that there is a newer version of the firmware for your Android 4 phone that will bring it back to the list of supported devices, you will no longer be able to access WhatsApp services with it.
Withdrawal of support for older generation Android devices is already in place for the latest version of WhatsApp beta. After November 1, phones removed from the list of supported devices will be able to access WhatsApp services using the version of the application already installed and previously connected to that account. Fortunately, upgrading to a new phone shouldn't be a problem, as the message archive is automatically transferred to the new device.