Appium 1.5 will have no new features. It is a major architectual refactor of the code.
So Appium 1.5 will still use the same Instruments approach that appium 1.4.16 uses today.
After Appium 1.5, we will be able to add the appium-xcuitest-driver. At first it will be a 'beta' feature, so users will have to send
automationName: xcuitest to use Xcuitest instead of Instruments. This could be added maybe in two months?
After we are sure that there are no bugs in xcuitest-driver and it has all the features of the old ios driver, we will switch the default driver for all iOS jobs to the xcuitest driver. This probably will not happen for about 3 or 4 months from today.
For now, users can install or clone the appium-xcuitest-driver and test it by itself.
The appium-xcuitest-driver uses the same Mobile JSON Wire Protocol that Appium and Selenium have always used. Your tests should not need to be changed at all except that findElementsByIOSUIAutomation will no longer be implemented. Right now there is no plan to add the ability to write custom tests in objective-c/swift. If there is a feature that needs to be implemented, please create an issue on the appium-xcuitest-driver repository on github.