I’d argue Senku hasn’t really accomplished much of what he set out to do when he awoke from stone. Tsukasa threw a monkey wrench in that “discover the secret of petrification and restart humanity” plan. It took 80+ chapters just to deal with that headache. 40 chapters later and the only progress towards that goal is “this new group has a miniaturized version of the petrification weapon”. Dr Stone has this uncanny way to basically put up a big road block (tsukasa, the master/ibara) between actually making progress on learning how and why the events of the series happened. Just like with Attack on Titan the basement wasn’t the end, but a new beginning for the series. That is what I expect the reveal of the truth of petrification and who did it to have on Dr Stone.I know, it's why I said "might". It's not as probable as some others and there's still no "final arc" announcement but it's not a series with too much left either. And it moves pretty fast, or at least it seems to to me. 124 chapters isn't that many considering all that has happened in the story.