SSZipArchive (or some form of zip) is needed for Tilemap support.
Also, iOS 5 is dead. Even iOS 6 is pretty well mummified by this time. Any work that goes into supporting an iOS version that's older than "most recent major version minus 2" is going to be a waste of time (even if it means leaving some devices behind). Except for certain fringe cases (ie client requires .. no, demands it or you really want to play your own app with you kids and the only other device in the household is an iPad 1).
This goes more so when you consider starting a project now and perhaps releasing it to the Store 5-10 months from now.
Yes, same old argument: "there are still x million devices running iOS 6 or earlier". For sure. But only a very, very minor percentage of them visit the App Store anymore to install new apps, let alone spend money on them. It's not worth supporting devices that you can't make money off, unless for certain non-monetary reasons (see above).
Point is, if work on Cocos2D should continue at a decent pace, Cocos2D itself must be a forward-looking project. It can be very time consuming trying to support older iOS versions, more so if it means also supporting (speak: building with) older Xcode versions. It's not just a matter of lowering the deployment target and testing if it still builds in Xcode 6.3. It also would have to build successfully in Xcode 6.0 or 5.x. For instance and if I remember correctly, Xcode 6 does no longer (officially) support building and running apps on iPad 1, you ought to be using Xcode 5 for that. Given how much the compiler changes in each Xcode version it's actually rather common to run into issues that only appear in certain Xcode versions, and whose fix might then not work in a newer version.
This is compounded by Swift, too.
OTOH for the individual developer who needs that backward compatibility any related issues can usually be fixed when putting aside some time to make the necessary changes and querying the net for answers.