In a scenario where you would like to cancel the sliding to a specific index, you should use the SlidingToIndex event and cancel it. However, this action results in freezing the control. Available in minor release 2017.3.1214. It will also be available in the R1 2018 release.
Currently, you can successfully add button or gesture recogniser only on UWP and iOS. On Android this approach causes the SlideView stop sliding.
The only way to customize the SlideView indicators is to predefine the SlideView ControlTemplate. Available in the R1 2018 release.