My company switched to a free slack account a couple years ago, from our own IRC server. The primary reason for the change was to get something a bit richer in abilities, and emoji reactions is something we make extensive use of. Just saying there are people out there that find these sorts of "XMPP breaking" features not only useful, but mission critical.
Would have been useful if their announcement included some of their data for reaching the conclusion, like "95% of channels use emoji reactions in more than 5% of their messages". The announcement, as it was, didn't read very well to me.