I've decided that i'm kinda on board with the whole Jon Snow/Meera Reed twins thing, precisely because there's so little reference in the books but none of the evidence refutes it, combined with GRRM taking a personal interest in her look when she was cast. The Reeds kids are minor characters in the novels that could of easily been dropped from the TV adaptation (and were, from season 2). They were introduced as new characters for the show this season yet have about 7 minutes of screen time so far in Season 3, and they aren't doing much to make bran's story any less boring, so why bother casting them?
It's similar to my theory that the Horn of Winter was found by jon buried with the dragon glass, and he gave it to Samwell not realizing what it was. It's only mentioned twice in the books, barely described so that the reader forgets about it. Once when it was found and just casually handed off to Samwell, and again when Samwell is selling shit for passage to Old town, the horn was the one thing he wouldn't sell and kept with him. Barely referenced and mostly forgotten by most readers, like the Meera angle, but probably true. More probable than mermen did it atleast.
GRRM put's a lot of prophecy and allusion and shit in his novels so people focus on the obvious theories, leading you to believe that certain characters are "untouchable" etc. It's just another way to convince the reader that those are the main characters so he can troll everyone by killing those characters off later. Jon, Dany, Tyrion, looking at you three.
Howland Reed was with Ned Stark for the entirety of the War including TOJ which means either she's one of his bastards and his wife gives 0 fucks unlike Catelyn when he raised her as his own trueborn child like Ned did with Jon; or his wife got freaky with the pool boy and had a surprise waiting for him when he got back from the war and howland gave 0 fucks about that; or that Lyanna gave birth to twins and Ned took one while Howland took the other, and he either told his wife or he didn't, and again, she gives 0 fucks about bastards. Given that his wife wasn't some high lord's daughter (iirc she was low born?) either Meera is Howland's bastard or atleast Howland claims her as his and wife don't give a fuck, cus I doubt he'd put up with his wife stepping out like that. All we know about Howland is that he was Ned's BFF and he saved Ned's life at the ToJ. But after the war they rarely see each other, howland never leaves Greywater Watch. Did they have a falling out like Ned and Robert did? It's never mentioned, yet he tells his children about his time with Ned before and during the war, like the tourney in the year of the false spring and the laughing tree knight, etc, so he still admires Ned and the Starks in general. Maybe they were they just trying to keep the children safe, and explaining one mysterious bastard child might be easy but explaining a 2nd of the same age that looks just like the first one? Keep them seperated. I went back and read when the Reed children were introduced and it makes sense. Her age, the way she's described, basically is like an older Arya, who looks more like Jon Snow/Lyanna than any other stark children. The night Bran meets the reeds he has a flashback to his father telling him about the ToJ, and afterward it talks about how Ned hasn't seen Howland since the war but about how they did communicate via letters over the years.