Documentation and education! That's why I really like the idea of https://readingbitcoin.org
There's a ton of "lore" and historical information that long-time devs have soaked up over the years but isn't clearly written down in a digestible format. When I've done some spelunking through Bitcoin history for articles I've written in the past I often end up having to sift through tons of mailing list archives and IRC logs which is quite grueling. It would be nice to have some technical writers take a stab at conveying more of this information to newcomers.