Shal, I envision it as a subsetting under "override, moderated" and therefore all their replies to other topics would be moderated, as well. I can't see that someone with this setting would not ALSO be moderated.
Oh! I was confused - I had thought you were going for an ability to let the member freely reply, but not start new topics without moderation.
You mean to moderate the entire topic not just the topic starter. That is, moderate replies by anyone to any topic this member starts.