The good thing about this is that the Chromecast is not supported by Windows apps whereas Chromecast has a number of apps in the Google Play store that support it. You can only use the Chromecast with Windows by using the Chrome browser to mirror the browser to the Chromecast. With a typical Android app, you can start something like Netflix streaming to the Chromecast then switch to another app without effecting the streaming content.
If MS hardware will be supported by Windows store apps, it could be more useful with a Windows device than the Chromecast is today.