Technical solutions would make HN less like HN, and more like Slashdot, Reddit etc.
My impression is that the elders I'm used to seeing are gone or holding back. Maybe they've found somewhere else they like better, or maybe they've resorted to email among themselves.
Whatever the solution, its goal would need to be to encourage more posts by wizards and elders, and discourage posts by, um, the rest of us. I think that would be most successful with social prompts rather than mechanical prods.
You might think about making comment karma visible again. With invisible karma, the only thing one can learn from karma is how bad one's own bad posts are. If you can't see others' positive karma, you don't have the opportunity to see how strongly other people like positive posts. "Dang, he got a lot of karma for that comment. I wanna be like him."
Or has hiding karma achieved what you'd hoped?