I am really, really terrible at finding things on HN, but I am inclined to remember things about social dynamics. Somewhere, he said something to the effect that he is being dragged into these arguments fueled by upvotes less often, so he feels that comment scores being hidden was successful in getting him what he wanted because he was spending too much time on that, so, no, comment scores are not likely to come back. You might look for some kind of follow up question of the Ask PG variety where people were hoping he would bring them back. It might have been something like that. (/Real hand wavy clues -- enjoy the hunt.)
https://news.ycombinator.com/item?id=1057347
> My plan for dealing with downvoting is just not to display points on comments any more. The hard part is that to make that work, I also have to come up with alternative ways for people to find the comments they're most interested in on big threads.
But as you say there's probably more to it than that. I'll have a noodle around with search later to see if I can find more.