Apple has recently announced that new and updated apps submitted to the Apple App Store must include 64-bit support for them to be approved. This change will be implemented by the Apple App Store starting February 1, 2015.
This means that starting at that time, Cordova-based apps should be built using a version of Cordova that has 64-bit iOS support.
The first version of Cordova to include 64-bit for iOS is 3.4.1. Therefore, to meet these requirements of the Apple App Store, you should be using at least version 3.4.1 of Cordova before this February deadline.
The 64-bit support for iOS is in the form of a fat binary that contains 32-bit and 64-bit code. This form of fat binary is only supported for iOS 5.1.1 and up. So when creating iOS apps with 64-bit support, you will not be able to target them for iOS versions earlier than 5.1.1.