I'm looking forward to Lemmy becoming a useful DIY or reference tool. I always used to finish Google searches with 'reddit' because someone somewhere will have asked that specific question already.
On top of that I'm going to miss those really supportive subreddits like r/dadforaminute and r/momforaminute. Though, it does seem like a lot of the people who made up subs like that have migrated here, so I'm hopeful!