Hello LJDawson, let me start with saying how happy I am to have Sync back :)
The one issue I have with Lemmy is duplicated posts between different communities (see screenshot). Posts usually have same title, author and link, yet differ in community/server they are posted to. It would be great to be able to make the appear as one item on the feed with some note below that links to both instances' posts, or something like that basically to make them not appear twice or thrice one under another.
I would imagine one post preview with a very compact list of instances on which the posts were posted so that you can enter either of those posts' view.
Or merge the posts into one view, show somehow it's a merged post, and merge comments as well (and let you choose the instance on which you want to comment if you create a new top-level comment).
Reddit had similar issue but it wasn't that bad since you hardly ever had 2-4 similar communities - something that appears to be very common with decentralised lemmy.