With Cordova-CLI 4.0 (http://cordova.apache.org/announcements/2014/10/16/cordova-4.html) you currently install cordova-ios 3.6.3 when doing cordova platform add ios
However this version doesn't support the iPhone 6 / 6+ splashcreens and icons - this has been fixed in a later commit as far as I can see (https://github.com/apache/cordova-ios/commit/5e136a09a1feae3b12309ee5b33854c18c853f86), and is therefore available in the master (or "nightly") version of cordova-ios on github.
As such, do you know if it's possible to install the master version of cordova-ios from the CLI?
Many thanks
You can use master from github until it's released:
cordova platform add ios@master --usegit