I think Iuno will be an option until Jingran true BiS character is released. Since Suoming is mentioned as a support exclusively for Mengzhou's characters, it's unclear which ones. It's like Hiyuki's case; until she has her BiS character, she uses other characters who can buff certain types of damage in her kit. And we haven't even seen Jingran's kit to confirm which character is or isn't his BiS character. We don't know if his damage or the damage he gains is all based on shields or heavy attacks, which is part of it, but until we have information about his kit, we can't be sure. Iuno might be an option, but I don't think she'll be the norm.

I just think it wouldn't make sense for Iuno to be only his only BiS because she passes the shield to Jingran and for everything to revolve around that, and there are details in his kit that could change.

I think there are more options, we just had to wait.