I've been to Quora recently, and I am totally addicted to it. I think some of the features on Quora can be used here.
We can edit any sentences in problems or notes if it contains any grammar error or wording problem. And if the author feels better after the edit, he can use it, else he can deny it. On Brilliant, we have moderators, but I think most of us can do this too!
I like the idea of Quora Credits. If this feature comes to Brilliant, it will be lot more better. We can use our points to do many things. For example, give it to someone whom you think their problems / solution is great. Or, when someone shares a discussion on problems many of us cannot solve, we can ask someone to answer, offering brilliant credits.
Writing an answer on Quora is much more convenient. This is an example on text box:
From left to right on the navigation tools are Bold, Italic, Underline, Heading, Blockquote text, Numbers, Bullets, Horizontal Seperator, Links, Insert image. On Brilliant, we have to upload our pictures to photobucket and get the URL, this takes a long time.
And the most important one, Save Draft.
On Brilliant, when I hit on a problem it will appear on the exact page with darker background. This is stylish and awesome. I don't know how other people thinks, but I always use "open in a new tab". This is because solving problems isn't like reading a story. I opened it on a new tab, and will attempt the problem for some time, if I failed, I'll leave it alone and continue searching for problems. On Quora, when I hit on any questions, it brings me to a new tab, so that I will always be clear which topic am I in. It's like a tree branch, keep growing and growing.
I rarely go on the homepage. Instead, I type a "." on the search bar to search problems. I think it's because the homepage is just slightly different from the search list. I cannot view a complete problem on the homepage or topic pages, I can only see the type of posts (problems/notes), title, levels and some words. This isn't make much different from the search result, so I think maybe the problems can be more complete on the homepage, like 10 lines. since most problems aren't too long. If possible, we can just solve the problem on the homepage
Phew, this is quite a length. This is just my opinions and suggestions. :)