Amy, that’s a tough one to answer without seeing the plan and what you want to show, but I’m happy to provide my input. I would tend to stay away from sub-projects if it is only for reporting. That’s adding a lot of complexity to the project. The rest gives you some options. If the timeline view provides a good format then you can do that. I’ve created multiple timelines for different workstreams, and in 2016 you can create multiple bars on the same timeline. You can print a pretty good looking Gantt chart if you take the time. I have an MPUG webinar that shows you how. The Reports menu can do quite a bit to provide graphs and the good news is that these are updated real-time. If you are more an Excel person than a Project person then yes, there is always an export to Excel.
The key I think might be to create a field called workstream that can filter/sort the tasks, and also allow you to select the tasks you want to report on.