Riot Games shared the details of their progress on Volibear's VGU, talking about the thematic, sound and VFX design and finally - the abilities. He will keep most of his identity with some goodies added in.
When League of Legends players think of Volibear, they think of an initiator that runs towards them on all four legs, is able to execute them and lightning everywhere. All these iconic parts of his identity will be preserved with the update but there will be a few more things that the kit will feature.
First of all, the initiator part will be preserved, as confirmed by the 200-year legend himself, Riot Lutzburg. Volibear will retain the ability to chase and lock a singular enemy down and is said to be nigh unstoppable as only death will prevent him from reaching the target.
As for the targeted bite, he will retain that too. What we have on the live servers at the time of writing is an execution tool that only deals significant damage when an enemy is already wounded while the updated bite will serve as both his opener and finisher. Furthermore, the stacking attack speed component will remain in the kit.
The chain lightning from the ultimate will still be here but based on the wording in the dev post , it seems like this part might not necessarily be his multi anymore. On top of that, the chain lightning is no longer limited by time and will end when Volibear leaves combat.
Apparently, the biggest innovations are put to Volibear's E and R abilities but the team was not ready to share more details on them just yet. Despite no more mechanics being shown, you can preview the new VFX of the E ability on the dev post linked above.