ESRI should develop various apps for the unified Windows 10 OS which currently are unavailable on Windows 8.x and Windows Phone; specifically the Collector app. Since an app developed for Windows 10 will work on both phone, laptop, desktop, tablet, etc. it makes more sense for ESRI to put the effort into developing said apps which is presumably why they were ignored for the Windows (Phone) 8. Being able to have a Collector app on the same machine as ArcGIS Desktop (such as on a Surface Pro) would be a very powerful combination.
This idea has been merged with Universal app for Windows.