They do make pull down shelves for handicap access. I have not seen something particularly for a mixer, nor that mounts that high or can come down that far.

Unless it were very heavy duty, and the mixer were bolted onto it very securely, I wouldn't want that type of thing in my house. If the mixer fell for any reason it could be tragic.

Are you sure you can't do a lower with a lift, or an appliance garage at counter level?