Ello launched back in 2014 with quite a stir in the US as it was about the time when Facebook changed its policy on names of its members, where they had to use their proper legal name. Its popularity grew as Ello presented itself to the world as a “Facebook killer social network” which doesn’t push ads down its users’ throats and doesn’t sell peoples’ information and data to 3rd parties.
A simple chat (slack style) it's enough. Just having the possibility to send messages either single user or team (#channel). But please don't forgive to give an useful appeal to mobile app (worst error of competitors is, have a good app but totally no mobile friendly!) i would expect to have a similar whatsapp or slack app for messaging within the slack mobile app!