I'd personally disagree with anything different for dodging champ select, it's the only time you can dodge from people that you know 100% will be toxic.
I'd agree with a TEMPORARY ban from ranked matches after hitting the loading screen. In addition to what the system already does (longer queue times), Maybe instead of an additional time based ban (multiple account workaround), make a game based 'ban'.
For example, if someone afk's enough often enough in ranked, they'd get a message saying that because they've been afk'ing their ranked games, they're temporarily locked out from ranked and they have the 10 minute queues. Then a quest would appear with something along the lines of this:
"play X games on summoner rift. Reward: unlock ranked"
I'd set X at 5 or so personally, but that's just a random number.
This way, if something that you can't control comes up (power outage), it's only slightly more 'punishing' than a normal afk game.