Browse a list of communities sorted by their Monthly Active Users (MAU). It could make discovering popular or active communities a bit easier. Just a thought! It's not something I'm really missing.
Add image hosting with an ephemeral approach like 4chan, where posts older than a day get little interaction and low-quality content is deleted after a month. This keeps a long-term archive of high-quality content without clutter.
A user setting to customize vote display: users could choose to see only upvotes for their own content, while viewing others' content by upvote percentage, or only upvotes, or see both upvotes and downvotes, instead of only total votes.
My ideal default would be, users have to subscribe to vote, because drive-by downvotes are very common, and keep niche communities from getting anywhere in the All feed.
Many posts don't have a language selected so 'content language' preference should either allow selecting those, or a setting to reverse it turning it into a block list with all languages automatically selected, then allow the user to deselect his language to block the rest.
Create a clear description of Piefed on the about page or another relevant page to direct users there instead of the code repository or specific instances.
User-created sorting methods: If the API exposes post metadata (e.g., timestamps, tags, upvotes, etc.), and the plugin system allows client-side scripting (e.g., JavaScript plugins), users could fetch post metadata and experiment implementing their own custom sorts in the browser.
I don't know which issues are urgent, I guess the ones preventing people from using the platform, but I don't know about any of those. These are just the ones I care about sorted by the importance I give them:
The votes don't show after reloading.
The markdown area where the posts are made seems a bit small.
Subscribe to anything. I believe that many users appreciate the ability to follow other users, similar to Twitter or Mastodon, and have a feed of new posts for the things they follow instead of an inbox. However, I don't like this approach because if you follow a few people with diverse interests, you'll end up with a mix of many topics in your feed. When you want to see something specific, it can be difficult to find. I think a better solution is to use content tagging and custom feeds. This way, users can have multiple feeds and follow different topics in each of the feeds. While this may make things more complex, the simplest thing for people might be to just follow and see it in one feed. A possible compromise could be to have a custom feed as the default for everything followed, and provide a way to select a custom feed other than the default one when subscribing to something.
Saved posts I think it could be better with collections of posts to have different saved lists for different topics. There could be a dropdown menu or popup to search or select a collection on a combobox with existing ones to add the post or comment to an existing collection or create it if it doesn't already exist. There could be a default collection to save things with a single click, like people are used to. This also gives the option to make some collections public and follow other users' collections.
Browse a list of communities sorted by their Monthly Active Users (MAU). It could make discovering popular or active communities a bit easier. Just a thought! It's not something I'm really missing.