That is a very sensible proactive move on the part of the team, they must have both been concerned about the future viability of third party twitter clients, and the potential of Mastodon as a new market. From what I've heard the Mastodon client they are building is very good, it's in closed beta right now.
I'm looking forward to trying it when more Testflight spots open up, it will be a day one purchase when released.
They’ve said they expect to release publicly by the end of the month. I don’t Mastodon much, but the beta is my only client and slick to use.