I think so many things are possible about this prophecy but right now I'm betting on Sansa or Margaery for the younger queen. "to cast you down and take all that you hold dear." if that includes Joffrey, which I believe it does because no matter what people say I still think her children are the most precious thing to her, then that probably means the young queen was involved in his death somehow, right? Dany, Arianne, Arya and Brienne (if the theory about inner beauty is right) can't be. I don't know how much Cersei is responsible for the prophecy's fate. Don't they say that the prophecy only becomes true because you believe it? Melara's death is very suspicious and it seems like Cersei herself pushed her. So if Cersei believes Margaery is the young queen her obsession might as well turn Margaery into that. She already started doing that on AFFC and ADWD.
Now the valonqar... I really really hope it's not Jaime or my feelings will crush me but it would be much more interesting than Tyrion. It hasn't been said if the valonqar has to be Cersei's little brother or just any little brother. But even if any little brother is possible I can't imagine him being many people because strangulation is a very personal death. Besides her brothers, I can't really think of anyone who hates her that much.
Yeah, I've been giving this too much thought.

Margaery is my bet. Sansa is not a queen, nor is she taking anything from anyone at this point. I mean she's certainly involved more but not really on Cersei's turf. I guess whatever happens to Cersei started with Sansa like a pebble starting an avalanche but I think Margaery has a more direct impact. And willfully so. And yes it includes Joffrey, Tommen, power... etc
I don't know if Margaery was involved in the plot to kill Joffrey. I think she's smart enough to know he needed to be removed and for not wanting him as a husband but even if she didn't, it was her marriage that precipitated his death since The Queen of Thorns was part of the plot and Cersei's fall from grace is caused by Margaery's later actions.

And yeah I agree that Melara's death served one purpose: to show how much Cersei is willing to do when she believes in something. At this point, she knows she has more enemies than allies, at least those she doesn't pay or threaten to be her allies so it can be anyone but since she's chosen Margaery as "the one", she's precipitating her own fate by doing so.

Get ready for it. Everybody thinks it's a red herring but I think the red herring is Tyrion, like Cersei believes. I'm very sure it's going to be Jaime. There's a symmetry in there somewhere. I'm not sure how we'll get there though. He is falling out of love with her and he's full of disdain, even ignores her when she needs his help but from there to murder?
But yes I agree it's a very personal murder, full of hatred. But then she pissed everyone off so I don't know. Maybe it won't be Jaime. My money's still on him though.

Yes, but I think there's so much more in Sansa we haven't seen yet. And now she has Petyr by her side, in a way, maybe it will be a weapon. But right now, Margaery sounds like the most likely

I don't think she was directly involved either. But her marriage played an important part in his death, even if not by her choice.

I'm really scared of what's ahead for her. She is her worst enemy and she managed to alienate everybody who could help her, even Jaime! And now Ser Kevan is dead, who is going to rule? The only Lannister who knows how to play the game of thrones hates her and Jaime. I think there's no way for her but down

I think it will be Jaime too. It's the only one that I can actually imagine fulfilling that prophecy. I have no idea how we'll get there either, but I think that if it happens he'll be dying. I think "We will leave this world together, as we once came into it" will end up being true. Even if he ends up hating and despising her, he'll never stop loving her and I don't think he can keep on living after killing her. And there's some beautiful thing about both Jaime and Tyrion killing the woman they love with gold. And Cersei Lannister dying through a hand of gold.

But even so... just put a knife through her and you'll have the same result.

Oh good! Ah! I don't know much about that one, but I think it's Jon. Being Rhaegar and Lyanna's son, I think it's very possible.

Maybe. I hope so. She's still very boring to me but she's learning so who knows?

Yeah I think it's going to be a long fall but it's started already and it doesn't look good for her.

a murder-suicide. Maybe out of despair? It'd be more likely to smother someone than to choke her but I'm waiting for it now.

Ooooooh nice! Never thought of that. And you're right, there's a symmetry to it that would be just like GRRM! And the prophecy was already mentioning gold in several ways. So...

I'm with Maester Aemon, I think it's Daenerys. She was born on Dragonstone (the smoke and salt part), she's the daughter of Aerys and Rhaella so you can't get any closer to that line, and she woke dragons from stone. Until Jon wakes dragons from stone, I'll stick with Dany
Dany already defied one gender restricted prophecy so why not two?
But I have seen credible theories that Azor Ahai might be more than one person and that the theory of the three headed dragon could mean Jon, Dany. and... some say Tyrion. I'd love that. I just don't know yet.