Hi Michelle,
This is in our backlog and on our roadmap. Unfortunately, we were not able to get to it in 2017 but I'm hoping we can target a release in 2018 for it.
Can you provide any details or use cases on why this ability is needed? I know that controlling the visibility of layers is a common task in mobile apps; but one thing we've found with Workforce is that, since the Workforce Projects are geared towards specific types of work, the need to control the visibility of layers is not as much a priority as other apps.
If this is something you'd like to take offline; feel free to DM and we can discuss.
thanks for your feedback,
Craig