Why?

The vanity would occupy the largest area especially in a smaller powder room.

Stick out as impressive or stick out as odd? I do think this is an impressive bathroom. I am not sure I like the pail for a sink in this particular design. If I was standing at the mirror would my head look like I was standing in the window?

IMO the mirror seems disportionately small and the shape of the mirror doesn't work right in the space for me.

Ok you asked for it. I usually don't offer suggestions unless someone is paying, mostly because people listen much better when they are paying. But anyway, when I design a barrell vault soffit like this, I play it up as an important architectural feature. So I would have either covered all of the space left on the back wall with either mirror or the same decorative tile on the backsplash. I would not have used a shape on the top of the mirror that fights with the arch. I don't usually make the backsplash this high either , but if I wanted to make a statement with it, in other words, play it up, I would have covered the entire back wall with it and hung a mirror that went down to the counter top and hung the wall mount faucet on the mirror. One other thing the counter top can follow the shape of the column detail on the base cabinet without projecting so far out that you run into it , someone is missing on the portions.

Just my professional opinions.