If we are to regard Lissandra and Trundle's lore interaction together as still canon (even how outdated it is).
We can safely assume that Lissandra has plans for the trolls in the war. Also according to another person, Lissandra is using the trolls to raid villages so that those villages will join her for protection.
However, I think that Lissandra will order Trundle to join the war where they will become a huge threat to Ashe and Sejuani.
A group of trolls are not a threat for both of the armies right? Well they wouldn't if they were just as tall as any human but they aren't.
Frost Trolls are giants. As seen in Olaf's fight everything comic and Call of Power. Now, imagine an army of those giants that are not only fast for their size but have an affinity with their environment.
The only way they can be matched is the Ursine but Sejuani with Udyr and Ashe are unlikely to bargain with them.
And when Trolls are unleashing chaos in their territories, Ashe and Sejuani would either band together or rely on the Frostguard's help.
When the trolls are ridden of at this point, both tribes are weakened and Lissandra could take advantage of them in her unknown plans.
But what do you guys think? Is it ridiculous? What do you think could happen?