Suggestions: A fourth...

1) A Fourth level of separation:

Category > Channel> Thread > Sub-thread
Category > Forum > Posts > Sub-post

The issue is that there are a lot of people out here that don't use Discord exclusively for gaming.
 
Some of us need a little more division, for example character creation: 
 - Lore [Category] > Species [Channel] > Subspecies [Thread] > Details [sub-threads]
 - Character List [Category]> Writer[Forum] > Characters [Post]> Facts [sub-posts].  
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2) The ability to re-arrange posts within Forums freely as you can channels.

Using these the way we do, we'd like to alphabetize them for example if there's a long list. Like I said, not everyone uses the forums the same way, and this modification would be helpful. 
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3) Dividers. 

When you have a long server, dividers go a long way to organizing a server. Right now you have to waste a channel or Category & Channel to do it (because they're invisible categories if they're not used, I've realized)  But to visually differentiate sections of a server. 

Create New > Divider
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4) Emojis in Titles (without cheating).

The fact is, the way people see things is color first. So adding color to the server list via emojis is a great way to make the server much more easily navigated. Again, this is a user-experience thing. I want my users to be able to easily find what they're looking for. 
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5) The ability to archive in-server.

This should be something that's native to Discord. Right click > Archive channel [location popup]
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6) The ability to un-read a channel rather than a post.

It's annoying having to actually click into a channel to un-read it. People should be able to do so without actually going into the channel. 

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7) Opt Out for the full-screen-image previews with Push notifications

The fact that this wasn't native, is honestly the most annoying thing. I'll be in the middle of writing something and [random meme] suddenly fills my screen interrupting my thoughts. What on earth were you thinking when you decided that was a great update? 

.. I think that does it for my suggestions. I'm putting this in “Other” because it covers a few things and I don't want to make 7 posts.