Since Noxus is expansionist, probably it wants to expand its territory. However, both Freljord and Shurima are harsh places. One is extremely cold and the other is a desert. Will Noxus be interested in those regions? (Or was Noxus interested in those regions?)
If you have questions about the Lore, you should ask them in Story, Art and Sound , from my experience, people are more likely to answer there.
"Attack" is a pretty strong word, but yes, Noxus survives by expansion. They sure are interested in both Freljord and Shurima, they even have territories on the Shuriman continent as seen on the map.
A bit more hidden, but Annie's biography along with information about the Delverhold in The Principles of Strength confirms that they send settlers in the north.
I don't think they'll declare an all-out war, but there are other ways cities or territories can be integrated in the empire.
I think the implication of Swain's "retreat" (I'm sure he wouldn't call it that) from Ionia is that Noxus is going to be focused internally for the next period in the lore. What with the Black Rose and all.
That doesn't mean they aren't expanding. Recent stories focus on their absorption of "neutral" territories. There's land between Noxus and Demacia, for instance, that currently doesn't belong to either.
