About it's sales in US, from my personal experience and my pals , in Boston 's noble and Barnes when went to buy the volumes the entire area was empty with only 3-7 copies lying and when asked the lady at that counter she said S8 got rapidly sold and now they've reordered more and keep in mind it was just the 2nd day . Not to mention that all over America in our GC people have claimed that S8 is selling well and in many places they are reordering it because of it getting out of stock constantly. This is my personal experience, also in Amazon US the first 2-3 days it had ranked 5th best seller.
Also in countries like Germany France Europe etc they have all sold well, I believe in Germany or France maybe they had sold 70K copies in just the first two days and got out of stock in just 5 days, which is why they issued premiered versions of the volumes and even battery chargers of S8, just recently maybe a few days back, a French user said that now it has sold over 150k copies. Other countries also have sold heavily like they always come in top 15 best sellers in those countries not to mention the people there loving it greatly.
Not confirmed if it's ending or not, but people all over the Twitter are saying so, also this latest volume 5 might cover upto ch 43 . So maybe S8 will be replaced by Kubo's new project