It's way worse than just the TOS change. Mandrill has a lot of advanced features (webhooks, reporting, AB testing, templates, etc). Some companies may be able to switch to SES or mailgun in a day, but more advanced integrations could take weeks. We're stuck with either pulling people off critical project in order to meet their ridiculously short deadline, or pay insane bills (the new price is over 4x the price we signed up for).
I emailed their founders and never received a reply.
Lesson learned: do not take a dependancy on MailChimp for any reason.