> We kicked off the project in earnest with a three-day in-person onsite for design, engineering, product and program leads. With the prototype as our guide, we started to sketch out the path to production. Which teams would need to be involved? How quickly could we move? When might we start bringing customers into the process? Which questions were most important to answer first?

"When might we start bringing customers into the process?" Seems like this should be much earlier in the process, no? Sure relying on automated metrics to help guide your process was part of the path, but if you aren't really talking with customers and figuring out what your needs are, your designs are going to be more biased towards how Slack operates and the culture of Slack.