Pinned for the idea. Not sure how much I like the extension over the toilet. If were to do, vanity top should be one piece, with no cut line. Also: Consider how much the extra counter space would be needed.
If you don't have a 2nd bathroom this is a possibility. I wouldn't buy a house without a second half bath. (I had a 1920's house that had a toilet in the hallway between the front door and the kitchen. You had to shut the hallway and the kitchen doors. Then you were in a bathroom; not the hallway. Crazy.)