I think the most obvious answers would be SHINee and Seventeen, just because I love interactions between them (Key and Seungkwan's dynamic has my entire heart). Though, even while I've already seen them interact and work together on stage, I'd really love to see Ateez and Stray Kids work together again. Also Kai and Taemin (well, those are not actually two groups but to members from two and well, also from the same group). Last but not least, I'd love to see The Rose to collabs with literally so many artists because I'm certain their musical style would go so well with so many singers and fellow artists.