Early worries I have as a journalist using Mastodon for #journalism:

1) Subpoenas & source protection: You're at the mercy of whoever operates your instance. I'm guessing most smaller instance admins aren't also lawyering up to protect newsgathering.

2) The owner of your instance can read your DMs. Be careful.

3) Publishers could effectively verify journalists by running instances from their official domains. They could surveil their journalists there too. Not every publisher is ethical.