but the cost is like 10-30 times that of other options

Are you just talking construction costs? How about if you consider the lifetime energy consumption of a building over, I dunno, 50 years? And using zero emission heating, since in 50 years we hopefully are not using fossil fuels for that.

Obviously that's going to vary dramatically depending on the indoor/outdoor temperature delta and future renewable energy costs, so there are too many variables to come up with a number easily, but I could see these bricks being very cheap if you factor int he total cost over the life of the building.

The better option than glass block would be filling the cavity of a double glazed window with aerogel granules

Glass works ok for small windows - but large glass panels are fragile and expensive.