My first post for this pairing wasn’t quite so obvious (except for my tags), so let me just say it here: I ship this. Really, I find it kind of silly for Moriarty to be playing with Sherlock when Mycroft’s just right there. Maybe it’s because it might be more.. fanciful with Sherlock? Where it’s like a game, whereas going up against Mycroft might feel more like an actual war? Cause Mycroft can do things. He is the British government, after all. And something about matching wits and resources on a full-on international scale is just really appealing to me.
It is a good point - why wouldn’t Moriarty be interested in playing his game with the powerful elder brother?
I do rather like the idea that playing games with Mycroft would quickly escalate into war. I bet Mycroft played a lot of chess as a boy.