A toggle option so that threads appear as "N comments" and open in the side-panel, so they do not interrupt the main flow of the channel, and you can follow each thread mode easily.

Implement off-the-record messaging (https://otr.cypherpunks.ca/)

Add feature to make video/audio calls (personal/group)

Now the contacts (Direct messages) are always sorted alphabetically. It would be great to have different options of sorting. What we like the most is sorting by last message recieved/sent, which means on top we always have our most recent conversation (like in Skype)
Any chance to have it in future?

right now in the iOS app if you setup an instance I do not see a way to setup another one and seeing as how the current architecture of the product is, I would need multiple servers for my org's needs. the app should be able to handle it as well.

Creating and participating in Polls would be great,
to be embedded within a message.
Like in Doodle, Facebook or Threema:

Option | User1 | User2 | ...
---------------------------------
Coke | x | |
Sprite | x | x |
...

OR

Option | Votes
---------------------------------
Coke | 3/15 Users
Sprite | 2/15 Users
...

For IT policy compliance, offer the ability to invite non-team members users to Mattermost as "single-channel guests" to have access to read and write to one channel and direct message any other users in that channel.

Potential scenarios include opening discussions with non-team members, including customers, vendors, partners and interview candidates.

This feature proposal is for the ability to encrypt posts/direct messages in the database, with a server-side encryption of the database contents.

Slack offers a very cool possibility: you can ask the bot to remind you of a message after some time.

This is *extremely useful* when you post a message which requires some reaction by some other users - if (unfortunately) no reaction comes, it is very easy to forget about the question, which will not happen if you set a reminder!

That would be a very nice feature to add to mattermost

With a lot of groups/channels ,the sidebar becomes very cluttered. A collapsable hierachy with sub-channels/groups would be great.

Or, easier to implement I guess, the ability to group channels/private groups into folders.

Sometimes a user posts his message in the wrong channel. Deleting the message and repost is a simple solution. However, sometimes the message already contains replies. Is it possible (to make) to move a message including its replies to another channel?

Add cusom user groups for mentions. Something like @developers or @frontend to mention all members of group in this channel. Also it would be useful for large teams, when novices does not know who is who - with this feature they can determinate at least group

Sometimes one's wondering if a post has already been read by other users. I could image that a member list of the channel pops up when one is selecting the read status from the particular post menu ("[..]").
In private chats, a sinple check sign (similar to whatsapp) could signalize if a message had beend read by your counterpart.

Most popular text editors change the text direction automatically to RTL (Rgiht to Left) when you enter a text in RTL languages such as Persian, Arabic or Hebrew. If that was the case in the Mattermost, we (the RTL language speaking people!) could use Mattermost much more productively, and localization to Farsi, Arabic, etc was possible.

Would be lovely to view the files that have been shared in a channel. This would go neatly with the idea of pinning posts as well. You could be able to pin files.

Add support for a generic OAuth2 provider for Mattermost Enterprise Edition, in addition to other single-sign-on features for enterprises.

As a user, I would like to be able to ignore the postings from other users. I would like to individually select which users I want to ignore. It should be easy to add/remove users from my ignore list.

Right now there's no approved way to do mattermost on ARM. I think ti'd be a great idea to fix that, and I'm working on fixing it myself. If I get a definitive result, I will post it in the regular forums and/or submit a pull request.