The good news is that until they update the game for USUM, this will be the last new Ultra challenge unless they decide to put the Primals here. Bad news being htat once they do, necrozma-dusk, necruzoma-dawn and necrozma-ultra will all almost certainly be Ultra Challenges. Which...great....I'm pretty much screwed against any of the Ubers now. Even with items. Most of the time I'm just trying to earn in game money and I just avoid trying to get any of them for the most part. It's not worth it.
Although Necrozma-U would make a pretty good final boss.....
In contrast the ultra beast challenges after nihilego (which was, i think we can all agree, an unmitigated disaster) have somehow become one of the better balanced challenges in the game. Since they have literal high cost barrier their stages have become easier, you get 10 tries, you get extra goodies and they became way less of a pain to take down.