Can you create a workstream or even an iteration without changing over completely to the Agile templates?

Hi Steve, 

Hope you are well.

This is a great question. It's my understanding that a Project object cannot totally exist in two different Project Management modalities. Mean, it doesn't really support both Waterfall and Agile at the same time. Separately, yes. You can create one project as a Waterfall. And then create another as an Agile. 

I suspect you project is set up to engage cross-functional teams or channel teams (you choose your marketing language of choice.:-)) Good examples of this is engaging copy, design, and web development. One of these teams works in sprints or agile. If there is one Project Manager that oversees the entire effort, you could utilize a "Work Request" Task. ie. Send to Web Team for Development. Here you can do a couple things. Easiest, and fits into WF's model, submit a request at the Work Request task to engage the Web Team. This submits to the Web Team queue. They convert to their preferred style of work management and seamlessly keep the ball moving (relatively speaking as I am unfamiliar with how your operations actually work). One benefit, as long as the request remains open and is not completed, so is your Work Request Task. This prevents the task and subsequent project from completing and promotes accountability. 

Bonus! You can even report on this to see what outstanding requests are out there for the web team. 

Hopefully, this is helpful. Let me know if you have any questions. 

Best,

Joaquin