For those who aren't aware, Aatrox caused the deaths of Tryndamere's tribesmen:
"(...) Raiders ambushed Tryndamere's clan in the dead of night, (...), they weren't prepared for the dark figure that next stepped forth. He wielded a cruel, living sword, and inspired an unhinged bloodlust in the invaders with his unearthly magic. Tryndamere's tribe was overrun within moments. With no hope of defeating the enigmatic being, Tryndamere threw himself at certain death. The dark figure swatted him aside, mortally wounding the young barbarian.
Tryndamere saw death and destruction engulf his home as his life slipped away. No one was left standing - only the screams of the dying remained. Unable to surrender to death, Tryndamere gave in fully to his wrath. His blood boiled and his anger consumed him, banishing his mortality. He staggered to his feet - barely able to take hold of his sword - steeling himself for the decisive confrontation with the shadowy being. But the dark figure did not even lift his blade, and instead gave Tryndamere a knowing smile as he withdrew into the shadows. That was the last time the barbarian ever saw his nemesis."
So, I was just thinking, it would be pretty cool if the Demonblade Tryndamere skin represented an alternative story where Tryndamere finally tracks down Aatrox and defeats him in combat. After Tryndamere crushes his nemesis, he takes up his blade (the Darkin itself). But this interaction is all part of Aatrox's plan to find a more fitting host, and Tryndamere, made vulnerable by his rage and thirst for vengeance, becomes fused with Aatrox, creating Demonblade Tryndamere.
Admittedly, the current art for Demonblade Tryndamere does not match Aatrox, but this art is a bit outdated anyways and could be changed to fit with this alternative storyline:
I think that it could actually look pretty amazing Aatrox inspired blade:
By the way, a story-telling cinematic like Varus received for his VGU would generate hype and probably increase sales of this skin by a lot. It could be really amazing if done well.