MacRumors reports that the Workflow team has confirmed in a recent customer support email there will be no further features but imply they'll do maintenance updates. Specifically, they wrote:

"But just so you know, we have no further planned updates for Workflow. That being said we are continuing to support Workflow's current functionality and have no plans to end support, so let me know if you run across any bugs or crashes."

We all knew this was coming. In hindsight, we should have known it was coming this soon. Whatever Apple hired the Workflow team for, it was not to continue developing Workflow. They've obviously already started on some sort of integration of Workflow-like tools in iOS.

However seeing it there, in black and white, that the app that I use repeatedly, every day, is now frozen feels pretty bad. I'm constantly writing new Workflows to automate working on iPhone and iPad. I currently have 53 workflows that I've written myself or boosted from somewhere else on the Internet.

Whatever Apple is working on, I find it highly unlikely that it will ship with iOS 11 that gets announced in just a few months. So my guess is we'll wait until iOS 12 to get the Workflow replacement, which is most likely 14 months from announcement and 17 months away from release. Will Workflow still function up until that time? I sure hope so.