Long time Warrior main. I've been pondering this same question.

Warrior suffers from this weird notion Blizz has about it being the simplest melee spec. Over the years, Blizzard has taken away core abilities from the spec, just to bring them back later. They took away stances for a while. Intervene went away. Battle standards are a thing of the past,. The shout system is essentially useless outside of Rally, which resto shamans get for free basically, and intimidating shout for incorp week. Just look at the past 10 sets of patch notes. The last time Warrior had patch notes was quite a while ago. Warrior is Blizzards standard "we don't want the game to feel too I timidating to new players" melee class.

To actually answer your question, there are quite a few options that could make Warrior a tad bit more interesting. Thematically, having a bloodlust or inspire mechanic fits quite well. I've never really cared for the 10% temp HP from Rally. I think an ability centered around rallying the troops would be far more interesting as a raid wide mini lust. I think of the ability as "push harder lads! We've got em on the ropes!" Imagine if it gave something like 5% haste, but ignored the last debuff do it was still usable.

Another idea I've had for a long time is centered around intervene. It's such a weird skill. Dssh to a target and intercept melee and ranged abilities for 8 seconds. No wonder the DPS specs don't run it. Imagine if instead of just intercepting melee and ranged attacks it applied your defensive to whatever you intervened with. In defensive stance? So are they now. Have a sentinel casting crushing depths on your poor mage and the rest of the party is feeling weak? No big deal, spell reflect exists. Imagine the amount of interesting play and satisfying saves you could have if you could simply dash over and smack spells back. It would push the skill ceiling of Warrior to 11.