Proposal: First wants to be about historical "firsts".
That's one thing History.SE is for.
That was my first impression.
If History SE considers anything that isn't a basic Wikipedia lookup on topic, I don't see how this proposal can go much beyond "Stuff History SE doesn't want."
That's just my early take on this.
I am not sure it is. A quick look finds the closed question. When did the majority of Americans stop living on farms? with the close reason:
While not a question about first, it would not be in scope at firsts, but it does highlight the issues. This appears to be custom close reason. Almost everything at "First" would fit in the category of "trivia or basic historical facts". Which appears to be specifically out of scope at History.se