The Stack Exchange Blog is a great place with a wealth of information but, as site ecosystems change, the content in the blog becomes outdated and can actually cause confusion. That doesn't mean that the information should be removed, though... as it gives the history of the site and helps us know where we've been.
I'm recommending that we create something like the Historical Lock banner for outdated blog posts:
This blog post has been preserved for historical significance, but it no longer reflects current policy, so please do not use it as reference for current site policy. [optional: For current policy on this subject, please see this more recent blog post/MSE post].
I know that this may be something that's difficult to address because there's so many posts, but if the most egregious of them could be annotated like this, I think it would be really helpful. It would preferably be linked to a newer blog post or MSE post that explains the current policy.
As an example, Joel wrote a post back in 2010 about the Beta ecosystem and explaining that beta sites would closed after a certain amount of time if they didn't meet certain activity guideposts. Since that time, we've come to see (as detailed in Ana's post in 2015: Graduation, site closure, and a clearer outlook on the health of SE sites) that low site traffic and questions are irrelevant to site quality as long as a site has active moderation. As of the time of Ana's post, no sites were slated for removal, regardless of low traffic numbers.
I'm posing this request because I do occasionally see users posting these outdated blog posts as reasoning for something or warning. Particularly with this one, I've seen users on Beta sites worrying that their site will be closed due to inactivity. I think their concerns would be tempered if they knew that the blog post didn't represent policy.
If others know of blog posts like this one that are grossly out of date, feel free to comment with a link.