I'm really just commenting on the design. The costs would probably be similar to box in the toilet with drywall vs glass and associated hardware.
A few years ago, I stayed with a friend at the W Times Square. They have glass windows into the bathroom and even though it's fogged, you get a pretty good idea of what's happening in the bathroom. They made a note of the fact that if you call the front desk, they have blackout panels that they'll throw up there for no charge. It's apparently a pretty common issue. We took full advantage. I'm guessing Yotel will have something similar. Hopefully the smell isn't too much of an issue. No blackout panel can eradicate the brownout smell.