In the original sense "that's a big ask" has implications that the ask is not practical and is received with a raised eyebrow. A bit like the quote from yes mi

In the original sense "that's a big ask" has implications that the ask is not practical and is received with a raised eyebrow. A bit like the quote from yes minister "That's very brave of you, minister. An extremely courageous decision," followed up by the explanation "Oh, yes! "Controversial" only means "this will lose you votes". "Courageous" means "this will lose you the election"!"