Whenever you look at op.gg you see "RIP" over Volibear. Which sucks, because I think the Ursine are cool and would love to play as him without feeling like I am trolling.
I imagine he may get reworked at some point, but honestly - a mini rework is all he needs to be a viable top lane pick akin to Trundle. (am not suggesting to do all these changes, but even a couple would make him better. Especially the change to his W)
Change 1) Add an effect to his Q, making it almost like Ghost. Only, instead of passing through minions, have it where he knocks them aside. It would make his engage a bit easier, make sense since he is a bear charging on all fours.
Change 2) Make it so the "bite" part of his W can effect towers. You did this recently on a champ, I forget which one. Maybe Illaoi? Don't remember. Point is, other champs like Yoric and Darius, etc etc can use their similar abilities to do extra dmg on towers.
Change 3) Add a .75 to 1s root on his E. The roar fears minions, great. Remove the slow and add a root. Is better for teamfights, and makes sense. Roar would scare a champ briefly.
4) His ult seems...lack luster. Instead of having it bounce, have it where the animation is that of lightning channeling into the enemy with every auto-attack. Doing continuous dmg and "shocking" them every 3rd auto, stunning them for .5s
Would look cooler, feel better, and let him lock down champs if built correctly.
Lastly, his passive. I like it kind of. Just wish it was a bit more interactive and fun. Feels like a garen passive only on a 2min cd. Personally, I'd like it if instead of a heal - have it to where he either takes less damage. A passive akin to doran's shield, minus the heal. Or where he becomes immune to slow once under 40% health. First would make his early game really good. The second idea (again, I don't want both. Would be one or the other) would make him a better duelist.
All changes making him a better top laner.
Just giving ideas. Would love to see him pickable, if not meta.