Does iOS support IPsec IKEv2?
I do not believe the built-in Apple VPN client supports IKEv2 on either the Mac or iOS devices. This is because certainly on the Mac - including Mavericks 10.9.1, and I believe also iOS the VPN client is based on the open-source Racoon software which does not support IKEv2.

There is a Racoon2 see http://www.racoon2.wide.ad.jp/w/ which does support IKEv2 but that is not what Apple include.

Cisco AnyConnect client for iOS and Mac does support IKEv2.