Blood elf rejoining the Alliace seem more likely than that.
His character wasn't a waste and he shouldn't have a redemption story because he didn't do anything that requires redeeming. He fought for the Horde when they agreed to kill the elves for him. The Horde didn't help him kill the elves, and then the Horde lost in WC2. Zul'jin was captured and tortured by the elves before he escaped back to Zul'aman, and now he's rightfully pissed that the Horde joined the elves.
You fail to realize or understand the level of animosity between the high elves and the Amani. They've been enemies for over 4,000 years. No negotiation, no trade, just kill-on-sight animosity between the two for thousands of years. To believe that he's a bad guy simply because he didn't side with the people that utterly failed him in the Second War, along with a race that he's been at war with for thousands of years, and that it's a fault that requires "redemption" is a ridiculous notion at best.
I spit on the horde
legendary line
I'm hoping for a troll expansion with shadow hunters. Not sure how it would work, but do want.
Zul'jin is a great character, but all his characterization is to be the enemy of the elves and humans, trying to revive the old empire.
if the elves were part of the alliance that would make sense but not as part of the horde, I think the Revantusk could get along with the blood elves because they are loyal to the Horde and its goal is to recreate a forest troll kingdom in hinterland, therefore the interests of Revantusk are not counterproductive to the blood elves.
I see Revantusk having more representation in the horde and the future are sub-race and as Jintha'Alor as capital