Dawn Wing Necrozma coupled with Prism Star Lunala played with Fighting Fury Belt and some cheeky Mimikyu tech is probably the easiest counter to Buzzwole GX, but whether or not we need a Buzzwole GX counter by the time this comes out is still unknown.
Dusk Mane Necrozma I think is a card that looks bad on paper (get it, cards on paper?) but honestly needs to be tested. Most people are leaning towards a 2/2 stage 2 Solgaleo GX split in the Solgaleo deck, which leads to a handful of its own issues in terms of consistency. Dusk Mane Necrozma's attack has the same "cost" as Sunsteel Strike on SuMo Solgaleo GX. Both of them discard 3 energy, which mean both of them have the same requirements for getting reaccellerated. It's just that Dusk Mane Necrozma has a higher "start up cost" with needing 4 energy to get going. Choice Banded, Meteor Tempest hits for 250 which is currently the highest HP any Pokemon can achieve in the game so far, so it really isn't a bad attack. SuMo Solgaleo's Ultra Road is great...if your opponent isn't playing Garbodor. Solgaleo Prism Star also makes the playing ground pretty even in terms of energy requirements.
Dusk Mane Necrozma gives the Solgaleo deck the option to play a 4/2/3 New Solgaleo GX line up and 3 copies of Dusk Mane Necrozma - New Solgaleo GX is your tank, Dusk Mane Necrozma is your sweeper. It's definitely not as streamlined as Ultra Road, but running better card counts might make the deck better simply through consistency.
Definitely worth testing.
Personally I can see both of them as tech cards in respective Silvally decks.
Dusk Mane Necrozma GX provides a soild ohko attack that the deck did not have in advance. I could see it replace Celesteela GX with Max Elixir and acceleration from Turbo Arm and Turbo Drive. On top of that Metal Silvally can also use Solgaleo Prism Star as a late game accelerator.
Dawn Wing Necrozma GX has a nice GX attack that blocks damage and all effects of attacks next turn and Invasion ensures that the deck will never be stranded with an active Silvally GX. The standard attack is at least decent. Psychic Silvally also has access to a lot of acceleration with Turbo Drive, Max Elixir and Lunala Prism Star. The latter on is also an excellent non-GX attacker. Include one or two Mimikyu and the deck looks rather decent.
I can also see Dusk Mane Necrozma as a one-off tech in Solgaleo decks but would not completely replace the old Solgaleo GX with it since it seems to need Ultra Road to deal with the massive retreat cost in this deck.