They didn't announced any possible participants but my concern goes to one of Mnet's own companies.
I know it sounds dumb but many people mentioned this on reddit before back as the trainees of Mnet's Japanese company Lapone Entertainment stoped using social media in September.
So Lapone Entertainment exists for the Japanese winner groups of Produce 101 Japan, but they also have trainees trought season 2 even tho these boys didn't won. Lapone sended them to Korea and they are there for over half a year now. They announced in September to stop using social media (Twitter, Youtube and TikTok) and fans were concerned. Basicly everyone said if they only take a social media hiatus to train for a possible debut than they are fine with it but if it's cause they could apear on Boys Planet 999 (since they are in Korea) everyone was disliking those thoughts.
I remember that I read on reddit how some people said that they might be fine with it if it's just for exposure but they hate to think how Mnet could make them join a KPop-group if they could be popular in the show if they apear on there. Other thoughts people had were that since they allready apeard on Produce and are trainees under Lapone that there shouldn't be a need to send them to another survival show. Also if they end up in the show people can't imagine what would happen since they know how Mnet handles editing. If they would edit them more handsome people fear that Mnet gets accused of favorism towards their own people and if they would edit them to look more ugly than people would accuse Mnet of sabotaging their own people to not make them look like if they would be superior or something.
>.< now that its official that Boys Planet 999 will happen, I don't like to think what would happen if any of the boys would apear on the show.
Those are the dudes I was talking about btw, for anyone who dosn't knows about them: