Let's use a compact 34/50 crankset as an example. With the direct drive, your chainrings are still 34/50 just like normal. If you shift the hub into underdrive, you effectively have a 24.8 tooth chainring and a 36.5 tooth chainring. Yes, it's not perfect integers, but the chain doesn't care because it's just a ratio. If you want to fly on a downhill, you shift into overdrive and your chainrings effectively become 46.2 teeth and 68 teeth. Duplicates? Sure. But whatever gear you need will be there somewhere.

I agree, the solution is not for weight weenies; it's for someone who needs a large range of gears.