It's not going to be more efficient in the end.

There's a reason that ad doesn't ever show the drive side of the whole setup. The mechanical complexity, eh whatever, it's still not exactly a complex system by any means

What it is, however, is a one person tandem bike. You can see the chain going from the handcranks to the rear cranks, they just fitted some freewheels along the lines so you don't have to engage them, I just checked another video where that's actually shown.

Imagine if they were fixed to each other however and then imagine how much power you'd really get out of your arms there that doesn't just get absolutely lost in the much, much higher power your legs put out. It's a neat idea in theory - additional watts from your arms means bike go fast, but the set up just doesn't actually work that way.

I'm not going to discount the idea entirely, maybe it's fun as hell, maybe it has benefits to coordination, upper budy strength and all but as far as biomechanical efficiency goes, it'll just make your bike heavier.

As for the future of bicycling technology, as far as sports go the UCI basically makes sure it never progresses into anything but what you see now as far as frames and drivetrains go. Mountain bikes still change a lot, though.

For everyday use, it's going to be the E-Bike I'd say. If we're taking a positive outlook, maybe Velomobiles. They're neat as hell and apparently due to them being aerodynamically optimized, you can hit 60kph on about 200 watts of power, which is what the average cyclist puts out on a ride. Plus you're protected from the rain and have a fairly large amount of stowing space. Neither price nor infrastructure is currently there to make them actually useful though.