There are a ton of threads about this idea. Unfortunately the difficulty is that kerf isn’t always the same from material to material. (Or even from batch to batch of the same material)
Therefore it’s really hard for Glowforge to make a feature like that that would work reliably. Personally I’d rather have no feature than one that is unreliable.
Just search the forum for “Kerf” and you can see the huge array of discussions. Here’s one particularly useful thread: