An Easier Way To Step Songs

I'm not sure if this has been thought of before or has been even done before but I was thinking one day that maybe we could think of an easier way to step songs. Instead of having to go frame by frame pressing arrow by arrow and taking a long time to step the song, the stepfile author will be able to start the song and there will be no arrows, it will be blank. To add steps the author will press the arrow on his/her keyboard when he/she wants to add an arrow to that specific part of the song. If the stepfile creator wants to add arrows that they cannot physically create themselves by pressing on the keyboard, such as some very fast jacks llike in Runny and CP, they can then use the StepMania way of creating those arrows and continue from there. By doing this, it will be a lot easier to step songs and it will be a lot faster.

Edit:
Sorry, this must have been done before, I should've looked at this further and seen if it's already been done.