100% agreed with this idea.
You said every little thing I wished someone to say. Yeah, the most broken thing currently in clash is the revenge system in lower leagues. For me and I believe you as well, want that the player desired to revenge gets kicked out if he/she doesn't have a shield and the live replay instantly starts (but now I would suggest for the prepared window appear showing the complete army before attack). If the player cannot be attacked, the message window will appear before the army window, making checking much easier. So yeah, I totally agree with you.