This gets ARKit working with ios 11 and xcode 9 official versions. But the camera display will be , I have raised this with the devs.
Install 4.18 Preview 1.
Create new project → blank → set it to mobile, no starter content, scaleable 2d/3d
Apple ARKit plugin should be enabled as default but just double check under plugins.
Setup IOS so your provision/certificate are present. Setup bundle display/name/identifier
Change minimum ios version to IOS 11, I’ve kept Metal v1.2, Frame rate lock to 60fps
Under Project settings enable ‘Start in AR’
Under Additional Plist data add this: NSCameraUsageDescription This application will use the camera for AR
Restart if prompted
In your game world you should have a Directional Light (mine set to static), and add a and a large cube static mesh (mine scaled to 100x100x100) set its world location to 0,0,0
Create a new Blueprint of type pawn and add a camera component to it, compile. Now add this Pawn to your world at position 0,0,0
Create a new material. It will be a standard material opaque/unlit and 2-sided. Add a Screenposition node and plug this in to the UVs of a ARKit Passthrough Camera node, plug the output of the ARKit Passthrough Camera in to the Emissive Color of your material. Compile and save this.
Go back in to your level and add this material to the Large scaled cube.
Build lighting if necessary.
Connect your iphone/ipad and Launch
Game should start but as I mention, camera feed is currently !! I have raised this with the devs as a possible bug, alternatively I may have messed up the process, but this is as far as I have got ARKit working with ios11