I'm curious if Slack ever considered using XMPP in their stack for core chat? As an outsider, it seems XMPP would fit like a glove (even signing in to a work "domain" screams XMPP).
I'm simply curious if the protocol was ever brought up in discussion and if there was a conscious decision to not go that route due to product needs.
I'm not going to speculate on what the advantages/disadvantages would have been as I honestly have no idea. I suppose if a competing product comes out that is XMPP-based then maybe we'll have some good comparisons. ;-)