Modern or Old version, i still don't consider Kyou a tsundere. True, she has the traits almost always found in those, but simply being violent and rash does not immediately a tsundere make. Neither do hiding/denying ones feelings - that would make 80% of all people a tsundere. Is Sekai from SD a tsundere ? As it stands now, i see her just as a girl with wild personality. While her behavior is a very good setup for a tsundere, she has yet to devolve to that state in my opinion. If else fails, use my racial ability 'Hate Tsundere On Sight'. I don't dislike Kyou thus far
Aside from hiding ones feelings not being a necessary indicator of being a tsundere, there might be a lot of reasons for her not making a move on Tomoya (assuming she has a thing for him, which is true, most likely), something like Ryou possibly having a crush on him as well. As pampering of her sister as she seems to be, i doubt she would make a move on him if she knew about Ryou having a crush on him.