Unfortunately, it doesn’t look like they are going to make that change.
As you noticed, the new V3 app has a different design philosophy for security features than the classic V2 app had.
Specifically, you can no longer automate changing the security.mode or unlocking a Smart Lock. See the community FAQ:
But feel free to use one of the official channels like the Twitter feed or the Facebook page to tell them that you would like to have this choice again. Because right now it sucks. 