Probably a hot take for everybody who just wants a drop-in replacement for Reddit, but I think a new platform needs to take the opportunity to improve over what's gone before.
So what I'm proposing is a more granular approach to curating one's feed on an individual user level, much like both Mastodon and apps for that platform offer (I'm going to use Tusky as an example because I've used that for a while and know its features fairly well).
Imagine a filter list where you could block specific terms, source URLs or other. No more irrelevant mentions of whatever annoys the hell out of you when you open /all. Along with your individual block list, limited as that is, it would help you as a user to home in on what matters to you.
Might this create filter bubbles? Yes, but if it's implemented on a per user level it won't affect other users' feeds. The "bubble" is a one-person act. In my experience /all on both Reddit and Lemmy suffers from people trying to curate it to their personal liking with downvotes, which just creates a monoculture.
Personally, I think free text filters would help solve that problem, and might aid users in engaging with their preferred communities. Suggestions, ideas?