You have UE3 for those devices. UE3 for iphone/ipad is not exactly the same as UE3 for pc/x360/ps3/vita, you understand that, right?
Besides, kepler is now expensive, it won't be in the next months when UE4 is suppose to ship.
Epic themselves believe UE4 won't be on launch titles and figure that they will come later, I can see in 2015 that mobile graphics chips (talking about laptops here) reach the necessary power for UE4, but we won't be seeing that at launch.
And correct me if I'm wrong since I've never touched the UE3 mobile platform, but is it just UE3 in name, or can you downport your projects to iOS from PC/PS360 titles? because if not then there really isn't UE3 on iOS.
Basically if they plan to support PC games in 2014, developers can't use UE4 unless it already down scales to Wii U's performance levels, because that is the majority of the PC market.
Just look at stuff like AMD fusion with it's 80 shaders to 400 shaders, it's performance is less powerful than a 360 when closed box operations is considered, and even trinity didn't catch them up... I really doubt the PC market would be ready to exceed the sort of power we are talking about, and I'm not even looking at UE3.99 using a 680GTX for it's demo.