I checked it out, but most of the public instances I looked at use google + bing. I think I only came across one that used Mojeek, but they deranked it so google results were still at the top.

Yeah you can customize them – if you never clear your cookies.

Pretty much need to self-host it to customize it.

we can get random experts chiming in about interesting topics in an organic way

1. In my experience, many of the people claiming to be experts on reddit are spreading misinformation. This goes for Twitter too, and probably most other large social media sites. People love to be seen as an authority on a topic.
2. Reddit is anything but organic, and is getting worse and worse in this regard.

Homeschooled kids are bad because they fart?