When this started rolling out it caused havoc for us. Without any warning that this was happening half of the people in our org got their display_name set to their full name, and the other half got their handle. For no apparent reason.

Within the technology parts of our org everyone knows each other by handle, and we still let people pick their own handle when they join. It's even pretty common to only know people by handle and not their real/full name. Monday morning and all of a sudden you can't ping a colleague anymore by @username, you have no idea why and now you need to know or find out what their first name is. Eventually that got fixed for everyone but it made Monday worse than usual.

I'm also not sure how this is going to interact with Enterprise Grid though. Since display names aren't unique you can get two people in a channel with the same display name. So if you now ping @John The Ripper, does it bug both, does it not go anywhere?