Yesss the Mikus are great, what a fun promotion. I thought about posting about it in the news thread
The art is done by familiar artists too. Take helped with character design Gen 7-9 and Mizutani is pretty prolific in the series being a TCG illustrator, Pokemon & character designer, and drew the official artwork for an assortment of Gen 6-on trainers.
Assuming they keep the music motif I'm guessing...
Poison: Toxtricity (literally a rock star pokemon, bet the outfit would be a mix of both)
Dragon: Altaria (song bird, owned by Lessia a performer)
Dark: Obstagoon (the singer of the galar band)
Flying: Farfetch'd (for the same reason its in the promo image: llevan polka)
Normal: Jigglypuff (the og singer)
Fighting: I'm going to go with Hisuian Lilligant or Kommo-o. Both are explicitly based on performance, so it just depends on if they want to go with ballet or haka.
Ground: Someone from the Tympole line; Tympole in particular has a slight music note motif and the whole line is based on vibrating and stuff, so I think that's a good thing to work with
Rock: So I was going to say Roggenrola, because even in Japan the pun is basically "rock and roll", but I'm going to pivot into a reference like Farfetch'd and say Rhyperior, because it shoots out rocks. Perhaps black ones. Like Black Rock Shooter
Bug: Kricketune (Conductor)
Ghost: Misdreavus (or Mismagius). I always kind of associated Perish Song with Misdreavus more than other Pokemon; if they went with Mismagius I think it'd be cute to have an Iono crossover
Ice: Lapras. It got associated with Sing so much it got a gmax entirely based around it. Mr Rime would be funnier though
Fairy: Diancie. Twin tailed princess with an extravagant mega form I dunno. Just kind of fits. World is mine.
Steel: There's not really a performer here, so they could go with something "girly" like Mawile, Magearna or Tinkaton. This might just be a "go with someone cool" type deal, so maybe Lucario or Gholdengo.
Electric: Pikachu sung once. we're not escaping PIkachu.
We're done with week 2 and the Mikus we got this week were
Electric: Rotom. Honestly I was goign to suggest this but I saw Pikachu and just resigned myself to fate. It makes sense as a choice since Rotom's got all those machines it can go into, the tech theme relates to Miku as a program.
Normal: Chatot. Jigglypuff really seemed like a shoe-in! Maybe it will be Fairy after all.
Ice: Lapras. Finally one I got right
Ground: Flygon. Now this was a surprising one, it's not one I would have associated with any sort of music theme
Seems like they based her outfit on Zinnia, too. Judging from the little bit of artwork, looks like Flygon is meant to use sand to put on a performance. Well it's fun that they aren't going with the most "obvious" answers
Rock: Aurorus. I'm kicking myself for not thinking about this one, they even kind of went in the direction I thought they would go with Diancie by emphasizing the fancy girly princess aesthetic
Flying: Altaria. I got the right Pokemon, but for the wrong type! I really thought Farfetch'd would win out because of the llvean polka, but I guess they decided to just keep that reference to the promo art for the album.
I'm really interested to see where they go for the remaining types, the design sheets are full of fun flavor and Pokemon interactions. What a fun promo