Same, I too saw the email and was able to purchase a membership this evening. Since it's coming up on the end of the enrollment period, I wonder if they are quietly doing an open enrollment to fill their quota. They've surely had a certain number of membership kits they've been working on. Perhaps they have a large difference in kits and current memberships?
Last year after the website snafu they randomly chose accounts on the sns site to offer memberships to and fill the quota. I presume that's what happened this time as I have an account and did not receive an invite, so it's not being sent to everybody.