What you're suggesting would be very helpful, but it's probably behind a lot of other things.
I did a clean up recently, & removed approx 80 or 90 people.
This process took like 25 minutes, & I was well over it by the end.
The problem was that every time you remove someone, the interface closes, & you have to begin again.
If clan owners were able to use for example a check mark system, then remove them together, it just saves so much wasted time doing the same thing over & over again.
I know these things don't pop up that often, so we can probably live with it, but if Jagex was able to make the interface not close every time, it would certainly add to my quality of life.