A really big thing that Cover needs to work on is finding ways to get the talents who are serious about live vocal performance out in front of real crowds for practice. Most of the major solo lives went on without a major hitch until Towa's where she was clearly really rattled. Those sorts of nerves can only be overcome by repeatedly getting out in front of real audiences and getting exposure therapy. The in-person crowds may be smaller than their streaming viewership but having a physical crowd greatly changes how you physiologically and emotionally react.
On the most basic level, think of the times when you were growing up where you'd try to show off something cool that you'd done a bunch in a game to someone and then messed it up a few times before getting it right. The smallest, friendliest audience can put stress on you such that you're no longer running at 100% with just an extra pair of eyes watching, let alone a 3-5k person crowd where you need to be able to sing, follow choreography, and keep smiling through everything.
The big challenge is, of course, not getting made in the process. Maybe a Holo-Club circuit where a chain of smaller 100-250 person venues could do a series of small solo-lives to get that time on stage in. Doesn't matter if you're pop, rock, jazz, metal, or whatever, but you need that stage time to get good and I don't want to see one of the girls feel like they need to quit or attempt a flip because they try to do their first solo live and just lock up when the concert begins. Stage fright is a hell of a thing and, if you've never been up in front of people, it's hard to communicate how powerful and unpredictable it can be.
