About 4 years ago, I was chatting with a journalist via Twitter and when we had to discuss details, he told me, "I don't check my email, just DM me"...which profoundly annoyed me. Now, I have to admit, if someone DM's me, I almost always immediately respond. Part of it is because DMs, for me, still pale in quantity compared to emails, so I naturally notice them faster. I think it also works because of why Twitter works overall...the truncated message length is both an impediment to communication and a lowering-of-friction...unlike email, I don't feel like I have to come up with a well-composed or complete response...nor should the DMer expect more of me (or else they should've gone through email).

So the group DMing makes sense...it's not an innovation, but continues to keep people in the Twitter system. Their photo app functionality had been crap for awhile, but between the extra steps needed to go through Instagram (nevermind the lack of previews), the photo app is just good enough to entice the user to not leave the Twitter app.

I'm surprised they haven't tried to implement Snapchat-like functionality, frankly.