I don't believe there is a key-in for this particular option. When you are creating a new linear feature, it is specific to a Field Book you are adding a linear feature into so you have to right-click and add a new Linear Feature through the Survey Field Book in the Project Explorer. You can have multiple Field Books loaded and there is no 'active' fieldbook. So I don't believe there is a way to add a New linear feature other than through right-clicking on the ALL Linear Features tab under the Field Book and adding the feature.
I generally use the search function in the key-in to find specific available values. I started by typing in survey... and it began to fill in the options when I selected the search function. Then I can drill down and see each available option for the commands through they key-in.
