It seems to me that Mastodon, tumblr, Wordpress, Threads, and any future platform's support of ActivityPub could theoretically make the entire internet "old Facebook".

Facebook is/was two things:

1) a microblog (your personal page)

2) an interface for following other's microblog posts

This sounds an awful lot like a following, say, a bunch of WordPress blogs in your Mastodon feed. We just need the interface over it all.

Heck, if Threads does what they say it will, Threads very well may become that interface for many folks.