If you haven’t received the email yet, it looks like the single sign on is coming 9/18.
I read through the T&C and it looks very similar to what eBay and other online sellers use. The Privacy Policy is interesting, but probably not much different than other retailers as well.
Long story, it’s either integrate accounts starting 9/18 or lose access to your account by the end of the year (which cannot be recovered – you’ll have to create a new one which integrates to your LEGO account).