I don't think it can regenerate hair cells because you need completely different pathways for that, but I do believe it can regenerate synapses and auditory neurons at least in theory and when you look at the science behind it should do that. NT3 is known as regenerative medicine that regenerates synapses and auditory neurons and improves overall auditory system.
I hit the plateau as well and it's strange since I think if it does indeed regenerate the synapses, plateau shouldn't be hit, and improvement should be gradual and not stopping in time, until most of the synapse damage is fixed. I've not been using it for long now, not even a full month and that 5-10% improvement was already a blessing to me even though it's not enough for me and my hearing is still pretty garbage, but it's definitely one of the positive things that happened in my life in the last few years.
Also using Astaxanthin with Lutein and zeaxanthin had a very positive impact on my eyes. I have less visual snow and fewer floaters after using it for almost a month. Also, the colors and visuals definitely improved so I think it does do something regenerative to the eye as well.
I think Curcumin working for tinnitus definitely has something to do with its anti-inflammatory effects since inflammation definitely negatively affects tinnitus and increased BDNF, but I don't have any working theories that would explain it in detail.