Do you know, I always had it in my mind that while H.G would (does?) do all the flirting, it's Myka who ultimately brings things to the next level. In Russia! Head!canon says Myka kissed H.G in Russia, but of course that could just be me.
I think Myka's more subtle then that though. I also don't really think she'd act on it till she was sure, and even then, she might not. Myka hasn't really had a serious relationship since Sam... and we know how THAT ended.
I don't know, I never really got the whole H.G tops all the way. I felt that H.G, for all her flirting, was too out of her element to really make a move...and Myka is more aggressive then we see, I think. But yes on the 'not acting until she's sure' bit. Or you know, they could go with a time-honoured tradition: make outs while piss drunk. At the very least Pete and Claudia would have had a kick out of it.
PS H.G. would be the one to make the first move.