sigh
"Don't explain the joke", they say... Man, I was being sarcastic. My point is that Scary Door threat was meaningless, and to illustrate I just applied it to the opposite side of the discussion. Then you asked me how it would work, so I said "just like it would work for the first side (which is to say, it would not)".
All in all, if you ban champions just to annoy people (and people in your own bloody team, I might add), you're an ass. You may not be reliably punished by the system for it. But you should expect other people being an ass to you in return and not getting punished either.
Also, as a side note: I may be naive, but I hope that the text area in the report screen is actually used by the system. If someone does something bad in champ select and nothing more in-game, I write in the text area what happened exactly, and if that's a big enough trend, I hope it would start being punishable. Or if someone does something that isn't actually covered by the current checkboxes, I check a couple of them that vaguely apply and I give a more detailed description in the text box. So, if I'm not utterly alone in doing that, any behavior that isn't detectable by the automated system can be punished thanks to the text description if someone does it often enough.