I have been pushing for Discord because

a) There is no need to host and maintain as Esteban said
b) There a ton of communities already using it and its by far the second most mature chat client after Slack
c) It has a very powerful Python API.... yes I know.... I know its no Pharo but still it makes it very easy to make bots that automate a lot of staff. I am using a bot that fetches RSS feeds (Although not sure how well this is working) connects to the reddit forum and of course fetches git commits
d) The team listens to its users
e) for personal reason.... all my favorite software (Blender, Unreal etc) is using it

I am also making my own bot . I�� could try to add a way for the bot to connect the mailing list with the Discord channel turn the mailing lists discussions to Discord discussions and vice versa but I have not done this before so no promises. I do have find a website that turns pretty much anything to webhooks which is what Discord uses (probably Slack too)

https://ifttt.com/discover

I could do the same with Slack , meaning to send Slack messages to Discord and Discord to Slack, I think I found one bot that already does this.

In short we can unite everything under one roof and let people keep using whatever people feel comfortable with (Slack, mailing lists, world.st forum, reddit , google hangouts , youtube , github and anything with webhooks or some form of web API)

Also the Bot could store its own log even in the unlikely scenario of a nuclear explosion in Discord servers we wont lose our valuable data. Though I think I saw somewhere that Discord allows to backup and export the data so that may be proven unnecessary.

On the other hand I will have to find a way to host my bot , but that is not a big deal , the bot is a simple python application and there are a ton of websites which offer hosting for python applications for free.

Its getting there but will need time.

Also my library Atlas can be used to access the APIs of all these chat software, Slack and Discord included, because Atlas allows you to use python libraries from inside Pharo. So its possible to have tools in the image for those of you that you love never having to leave the image that take advantage of these technologies. I wont be doing this though because a) porting APIs is a project by itself b) most of the code I find is python code and that makes it an easy copy paste approach (the vast majority of it is GPL or MIT licensed)