1- I don't think a really sick child is a good idea, just comes off as poor taste. It's one thing to have Nunu and Annie, it's another to have sick kid. Also, he'd step of Twitch's toes.
2- Nah, she came off as normal girl who snuck and freed him. She wasn't riding a yeti or burning people with a giant teddy bear.
3- While Noxus has shown death isn't the end of things, Sion and Urgot. I think a 3rd undead champion from Noxus would be pushing that theme a bit. I think he is more viable of a choice than both 1 & 2 though.
4- Yep. I'd say they will make her in time. I mean she is the 3rd member of the Ashe/ Sejuani/ Lisandra story. Not sure why it has taken soo long though.
5- Egh, I don't think so. He seems more like a background/story character like #2 does.
Zelos- He is up there with Lisandra imho. He was in charge and trained to fight. He fought alongside Irelia in her League Judgement. He really should of been created by now. He could be the Garen/Darius/Jayce for Ionia except with his own flair. As he knows how to fight with blade and martial arts. Plus I could iamgine him being a younger and cunning fighter.
Old Witch- The one who killed Vayne's parents is always a decent pick for a new champion that breaks the female mold. There's a chance LeBlanc did it under an illusion. But, LeBlanc is quite elaborate, if she did this... did she know she'd create a little dark magic killer nutcase that is Vayne? Or did she take on the appearance of someone she wants killed and is using Vayne as a chance to do so?
Ruined King- The original leader of the Shadow Isles, I think he could make for a pretty awesome champion. Though seeing as the King of Demacia stays out of the League, maybe this king will as well? But, I think he will have to have some huge part, I mean it's possible he literally ruined the lives of everyone on the Shadow Isles and turned them into what they are now.
Another Troll- Be interesting to see what one would look like without the curse and Trundle is also said to be a runt. As said in the judgement, Trundle's people will die as they now actually NEED the curse to survive. Maybe bring in one of Trundle tormenters (he was bullied) and have him seeking to drag Trundle back to save his kind. And it would be rather poetic. The mean, nasty troll who now is normal looking is the hero looking to bring Trundle back to save everyone while the once nice, noble troll who is now a monster is the jaded villain who doesn't care if his race is killed off.
Kat/Cass's father- Pretty sure he is dead. Would add extra driving force to both of them and Talon to over throw Swain if it comes out him and LeBlanc made him disappear. Which really, it sounds like they did.
Just some of my own thoughts.