Seems like it's more about finding ways to target users who have unsubscribed from a mailing list. That has its own thorns, but a sly price hike doesn't appear to be one of them so far.
[0] https://mailchimp.com/help/about-mailchimp-pricing-plans
> As a current user of our Forever Free plan, you'll now be in the new Free plan as long as your audience size is 2,000 contacts or less. The new pricing structure is based upon the total number of contacts you can market to, which now includes unsubscribes and customers who have simply not opted-in yet. You can check your Mailchimp account to see how many contacts are in your total audience. And keep in mind, you can always archive contacts you aren't using. On June 15, 2019, the pricing change will go into effect if you have more than 2,000 contacts.
So it sounds like it very much does change pricing on June 15th, at the least meaning previously Free users will now have to pay, unless they go in and manually archive unsubscribed emails.
> You can remain a free user so long as you have 2,000 or fewer contacts in your audience, and you’ll now have the new free plan features. If the new way of counting contacts causes your audience to exceed 2,000 contacts before June 15, 2019, we’ll automatically archive your unsubscribed and transactional contacts. After June 15, we’ll begin calculating your audience as described in Section 7B of our TOU, but you can always manually archive contacts to keep your audience under 2,000 contacts.
> If you are a current free user You can remain a free user so long as you have 2,000 or fewer contacts in your audience, and you’ll now have the new free plan features. If the new way of counting contacts causes your audience to exceed 2,000 contacts before June 15, 2019, we’ll automatically archive your unsubscribed and transactional contacts. After June 15, we’ll begin calculating your audience as described in Section 7B of our TOU, but you can always manually archive contacts to keep your audience under 2,000 contacts.
So it sounds like they are actually automatically archiving unsubscribed emails if it puts you over the limit.