ADA Standards and Coolness - Can they co-exist?

I'm struggling with similar concepts, though I'm not officially constrained to a single navigation option. I'm just starting out with making my (software simulation heavy) courses more accessible. 

You said you can't have two nav options, but does that mean you can't have additional options available to anyone? For example, could you put an optional link on a video slide that opens a layer with a text-based alternative/description? I'm thinking of adding a small icon to a corner of my slides that wouldn't work a screen reader, then setting its alt text to something like "Press Enter to access this slide/interaction/video with a screen reader" and putting it at the top of the tab order. 

If that's not an option, you could replace a drag-and-drop with a "select each image that applies," being careful with your alt text and tab order. If the user presses enter while tabbing over something, it counts as "select." Also, is it possible to add additional screen reader instructions to the alt text for an instruction text box?

Some side notes:

• From what I can see, objects on layers are lumped into the same tab order list as the rest of the objects on the slide. You could play around with the order there or just remove layer objects for simplicity. I haven't figured out how to get the focus to automatically jump to the layer, but I'm using NVDA, which is not a supported screen reader.
• Sliders are supposed to work with the arrow keys, but I haven't tested this myself.
• And just linking what's already out there: I'm starting here, and this ebook is at the top of my reading list.