WiFi calling in Android 6.0

Alright, so this may be a question nobody could answer for sure yet, I asked a Google rep this and they dodged the question COMPLETELY (lol). But I'm running the Latest T-Mobile build on my nexus and it has their WiFi calling added! Works great! But I was wondering if Android 6.0 would support native WiFi calling or if there would be a special T-Mobile build with the feature added! Any insight? Like I said however, this may be something nobody knows for sure until the release date of Android 6.0 Marshmallow!

EDIT: Just for laughs, lemme tell you what the rep did, he told me it was added and he told me how to activate it right now! (On 5.1.1 lollipop!) Dodged my question completely haha