In my opinion glass block is pretty dated. Perhaps a high clerestory window near the top of the wall to make it feel less caustrophobic and bring in light?

I wouldn't do the glass block. I think it would be a little weird if you're in your master bathroom and someone else is in the powder room. Even if you couldn't really see each other, you could hear each other, or be aware of each others' presence. Incomplete privacy.

You can lighten up the room with paint color and lights. Powder rooms aren't meant to be spacious places to relax under natural light. They're meant for doing your business and getting on with it.

Can you put a solar tube in the powder room? It give good (and free)light.

Lots of powder rooms aren't on an exterior wall and don't have windows. I wouldn't worry about it at all.

Another vote for no.

I put a sun tunnel in my yet-to-be-completed powder room. Another option might be a transom window.

I think it's a matter of your taste. I think glass blocks look cool, but the solartube would really add light and be "green", efficient and more modern. If you do go with blocks, I read somewhere that they are super heavy and you really need strong floor supports to use them.

You could do a row or two up high so privacy [perceived or actual] wouldn't be an issue, but I personally wouldn't: very half baths have natural light, so people aren't going to be expecting it.

You do want a bath or two with natural light for when your power goes off, though.

HI, we have no window in our current powder, in the house we are building we put a transom window over the door, the ceilings are 9' so we have plenty of room to do that. The door and transom face a bank of exterior windows so we are hoping that will let some natural light in. But it isn't something we especially missed in our current house. I wouldn't vote for the glass block, for what its worth.