One thing that I like to draw back to is that the Ursine have a shamanistic culture, and as such you'd expect them to have some magical practices but perhaps have them as being vary bound by traditional and tribe law, though I'd also imagine any Ursine could potentially become a shaman given their potential latent magical powers. Looking at trolls the reason why they probably don't use a lot of magic is because they're usually too focused on smashing and haven't developed as a culture enough to build any sort of magical practices and traditions. That and they're also often kinda...simple so to speak.
Food for thought, as a bit of story potential I like to drum up for Trundle is the idea that, realizing his own power and the potential for his people, he has secret expeditions put in to the hidden places of the Freljord to find ancient artifacts that he himself or his most trusted confidantes can use, bolstering his forces with magic; something pretty much unheard of (as far as we know) for trolls in League.
Going back to the Ursine for a moment, if the line of thinking that Yeti's could be spirits holds any weight, then potentially the Ursine with their shamanistic culture have Yeti's as a part of their belief systems, perhaps they even revere them. Makes me wonder what kind of spirits are associated with the Gelid Vortex or whatever the scared storm is called now, and how the Ursine remember the Frozen Watchers, if at all. Given their isolationist attitudes I can't imagine Lissandra as having taken any historic information that they would possess on the subject, but I could be wrong.
Also one final point; the Freljord's a highly unique place in Runeterra not only because of the ice magic, but also because it's the only place in Runeterra where humans aren't the sole dominant sentient species, and actually have competition with other sentient beings, namely the Ursine and Trolls. It's something that nowhere else on Runeterra has as far as we know since Yordles are either in Bandle City or hidden from human sights, and the other species like Marai, Minotaurs, Darkin, Brackern and whatever the sod Fizz's people are called are limited in population and environments in which they live.
or 
. Being a spirit would also explain why he has his ice ult and why nunu's snowball does more than what a normal snow ball can do. Lore wise, they could make it so Nunu could be chosen by the Ice spirit because of his affinity with the cold or something.
Definitely something Riot should think about for Nunu's lore update.
