Just want to give my two cents on this.
I think Blastoisinite is actually worth a mention for Darkrai - not only does it give a 50% boost to Darkrai's main STAB, effectively making it a Ghost-killer, but it doesn't harm its Speed stat either like Cameruptite would, and besides, Cameruptite is a nice stone to have free, as it can be applied to some of the most broken Pokemon in the tier (i.e Magearna) to aid it. It doesn't change much more from other sets that have been mentioned, so the same bread and butter idea is applied.
Honestly, in my opinion Darkrai is kinda bad in this metagame at the moment, and it's a shame, considering I've been wanting a strong Dark type for ages. It's easily revenged by Pixispeed, and REALLY hates the massive prominence that Magearna is having on the metagame at the moment, with Cameruptite only being able to break other Cameruptite Magearna with a 6.3% chance if hazards aren't up, making it extraordinarily risky to play with. These reasons only really give Cameruptite, Blastoisinite and Diancite room to breathe in the metagame. Absolite isn't really changing much other than the fact that you're revenged by Naganadel and Diancite-wielding Swords of Justice (Terrakion, occasionally Cobalion and Keldeo) now, and the slight loss in power and lack of a strong revenge killer isn't worth it for me, IMO.
Shaymin-Sky on the other hand is actually pretty good. Its typing doesn't do it any favours, yes, but it's the coverage and signature move that it possesses that make it much better than Darkrai atm, as well as access to one of the best utility moves for Bulky Offense - Healing Wish. That niche alone, combined with the ability to revenge all variants of Naganadel make it a premier pick for these sorts of builds, actually competing with Naganadel itself. I see Diancite being the only real set around - whilst Cameruptite might be cool, especially as a check to Lucarionite Zygarde, I don't see it doing much more than what Diancite already does - a strong revenge killer that isn't setup bait for Steel-types like Magearna and Necrozma-Dusk-Mane. That alone actually makes it rather hard to switch into for most offenses, and combined with HP Ice over Air Slash, it can actually carve into secondary switchins like Zygarde. Seed Flare also makes it extremely annoying to deal with, especially with that SpD drop - which can allow it to shuffle with Arceus formes - even Sablenite variants of Zapdos dislike having to deal with Seed Flare SpD drop -> HP Ice - which has a chance to KO physically defensive variants - and don't even talk about if Stealth Rocks are up, that will be able to spell the end for Zapdos if that does happen. Whilst I do admit, depending on the special defense drop is not the first idea I'd have when looking at Shaymin-Sky, it's one of the few Pokemon that can actually go past its counters that way - and 40% isn't that uncommon of a chance either.
Overall, both are fairly strong offensive threats, but the metagame just isn't in Darkrai's favour at the moment. Magearna and Zygarde are arguably the two most dominant Pokemon in the metagame, and because of that, Darkrai isn't really able to break through most offenses, and stall is usually bulky enough to deal with it, with Blissey being extremely common place - this isn't to say that Skymin struggles with Blissey either, but if it does encounter that MU, then it still has utility throughout the match rather than being a mediocre wallbreaker.
One mon, however, has been seeing some increased usage lately, and it's thanks to these new metagame threats alongside the rising popularity of OTR + CM Magearna that
Ho-oh has become very good in the current metagame. Not only does it gain these two Pokemon to check, but it checks old problems like Arceus-Ghost for a team. The only problem with that is that it isn't synergistic with Blissey, part of the reason the hazard game is so difficult at the moment. It has also benefitted a lot with the Pidgeotite ban - most of the Pokemon using it had some coverage to hit Ho-oh in some way, and now it finds itself as a safer switchin to Pokemon like Mew and - whilst risky, Genesect too.
