is it possible to witness another slayage solo debut of every single member (like BLACKPINK) from any KPOP group in future?

Impossible with the way MHJ is promoting the current biggest gg, I can see aespa having the GP hype for their solos if sm starts giving them more and more solo activities other than music and and don't let them collaborate with any other artists till their official debut to sustain the hype.

You mean digital charting right?

for album sales, they can have a bigger number than some soloists, but I feel Gen 4 doesn't have a strong solo image.

so a no from me.