Kingdom had great performances, but everything else was boring. There were no good storylines behind the scenes, so you might as well have just watched the performances on Youtube and skipped the show. Obviously, this is bad for Mnet. The following groups are plausible, great performers, popular, buzz worthy, have a good variety, and would come with interesting storylines:
IOI (Whoever they can get, but at least Somi, Chungha, Sejeong-hopefully but drama, Yoojung, Doyeon)
Storylines:
Itzy vs. Somi (IOI) - Somi leaving JYP (and Itzy) generated huge buzz, and this would bring all that back up
IOI vs. Kep1er - old vs. new Mnet group
WJSN vs. IOI - Yeonjung competing with her old group (best if Sejeong is in IOI, main vocal vs. main vocal)
Viviz and Yujin (Kep1er) - older idols starting in a new group after disbandment
Loona - more popular than Dreamcatcher and Chuu's variety skills would be good for the show
Dreamcatcher - great performers would make for a good dark horse storyline
Kep1er - can the baby group compete? Yujin is a veteran, so the debate would be interesting
Bonus: cute interactions. Many members of the groups have personal connections with each other (and not just Somi).
Plausibility. Reasons for joining the show:
M - Mnet's reason
G - group's reason
Viviz
M - for the big older group position (at least part of it) and the GFriend fans
G - great promo for their new group
Kep1er
M - big and growing younger fandom. Ive would be better, but that's probably not happening. The controversy of including them would generate buzz for the show
G - They have recent survival experience so they could do well enough to push themselves past Ive
WJSN
M - solid older group with consistent sales, like S1 contestants. Good performers. Pretty much confirmed already
G - would benefit greatly from the exposure
Loona
M - bigger international fandom than DC. Great performers. Dark horse storyline. Chuu's variety skills
G - need the exposure. Company spending too much and struggling
Dreamcatcher
M - big international fandom. Great performers. Different style for variety. Dark horse storyline.
G - could use the exposure. Stated in the past that they want to go on S2
Itzy
M - they're Itzy
G - last comebacks didn't chart as well, and Stray Kids got a good boost from Kingdom
IOI
M - older Mnet group that would generate huge buzz. Help salvage Produce brand. Could compete with Itzy in votes
G - complicated. depends on the individual members:
Somi - Wildcard. Could be into it as a great chance to reunite with IOI, perform in a group again, and maybe build back her Korean popularity to its previous post-IOI peak (most of her endorsements are Korean), or she could be too busy with building popularity in the West (and Teddy would be against it). Could be the "Crazy News" she has been teasing
Chungha - Likely. Could use the promo after last year's mediocre performance
Sejeong - Maybe. Her music career could use the promo, but she is working on a drama at the same time (not sure how much has already been filmed). Some members of SF9 pulled that off last year though. Also, Mnet recently posted her 'Warning' performance as part of their Fighting 2022 Special with a bunch of very popular artists, so that might be a hint
Yoojung, Doyeon - Very likely. Weki Meki could definitely use the indirect promo.
The other members seem very unlikely because they don't have music careers or are in China/WJSN.
If they can get the above members, it would be a great and well-balanced group.