"We've been experimenting with a different approach to ranked during early development, we expect to iterate on it in the future," a Valve developer known as Yoshi says in a blog post. "The focus of this mode will be on concentrating players into specific time windows where they can opt into games where the primary focus is game quality."
There's an updated UI after you select Play after the recent update which, instead of just throwing you into a casual match, lets you choose between the standard mode, against bots, private bots, sandbox mode, a custom match, and soon enough, ranked play.
Ranked play will open on Tuesday, October 15, at 7 pm BST/ 3 pm ET/ 12 pm PT, which means players still have time to prepare themselves for the upcoming challenge. You need to complete 50 matches in Deadlock before you're let into ranked play. 50 may not seem like a lot, but Deadlock matches can go on for an age (I've been in hour-plus games before), so if you haven't hit that number yet, you should probably play some Deadlock over the weekend. But if you have any "behaviour-related restrictions," then it doesn't matter how many games you've played—you're barred from entry.