That wasn't it, but the average line script with the straighten option selected looks just like the script I described. That script collection also has a bunch of other useful looking scripts.
I remember seeing a video or gif of a maya script which aligned vertices based on the first and last selected. ie: a line of vertices would be selected, and the 1st and last would stay in the position they are, and the ones inbetween would be aligned along a line from the 1st vert to the last. I can't remember where I saw…
Just bumping this out of curiosity, the ZHCG_polyTools are doing the trick for what I wanted, but just wanted to see if anyone knows the script I was referring to initially.