I was on that plan and I recently received the email. Here's the exact wording:
We recently learned that you received an email incorrectly announcing your Unlimited Photos plan was being changed into an Unlimited Storage trial. We're very sorry about this. We meant to let you know that the Unlimited Photos storage plan is no longer available, but you can continue to use your plan until it ends.
To make up for this, we are giving you 12 free months of the Unlimited Storage plan, which lets you store as many photos, videos, and other files as you like. When your promotional Unlimited Storage plan ends, you will be charged $59.99 for a one-year plan. You can cancel your promotional plan at any time.
This offer is valid until your current plan expires. Please accept this offer on your “Manage Storage” page: https://www.amazon.com/gp/phot...
We apologize for any inconvenience this may have caused.
Customer Service Department
I will take the freebie but not sure if I'm going to continue after that. I have 2.5TB of uploaded RAW photos. It took a while to upload that and it sucks that I may have to do it again. The freebie will expire in 2018 so we'll see what's available at that point.