It's an interesting approach, and here's why I think it's a bad idea.
Scripture implies curation and canonization. In the literal sense - an authority chooses which texts are foundational to a belief set. Rationality has no such authority (not even the authors of the examples given). In fact, rationality includes a belief that any attempt at such authority should be viewed with skepticism.
Haha! I love your first line.
I understand what you're saying, we don't have or want a prophet, and there are all kinds of things we believe that we wouldn't want to canonize. However, there are a few things we all agree on right? Bayes Theorem + Gathering Data + certain rules of inference + ...?
basically required reading so that we can have a community with a fixed starting point
What exactly do you want these "scriptures" for? The culture is not the "doctrine". Let's not conflate the two.
If you want to join the culture, the only way is to interact with it enough to let it rub off on you. This takes time. HPMOR is a great introduction to it, but the other sources you mentioned also work and they're not the only ones. It doesn't particularly matter where you start, as long as it holds your interest long enough for that osmosis to happen.
The "doctrine" is perhaps easier to distill, but the distilled version is not always easier to digest. Inferential gaps are a real problem. The Twelve Virtues of Rationality is such an attempt, but it's a terrible starting point IMHO. They don't make sense unless you already understand the principles behind them. They're better at helping you remember things once you already start to "get it".
I put "doctrine" in scare quotes because even calling it that puts it dangerously close to certain failure modes we warn against: "If you speak overmuch of the Way you will not attain it." I feel like saying "our doctrine is that we have no doctrine", but that isn't quite right either. We have two core principles, plus some key insights that most of humanity currently lacks. The rest follows from that.
The first principle is "self-honesty" or "Epistemic Rationality". Study not the capital-T "Truth" which the deluded and the deceivers will say they already have, but the methods that lead one to it. I have found no better illustration of the correct attitude of self-honesty than the Litany of Tarski, which is a template you can apply to any claim, especially claims one might be inclined to take personally (e.g. "God exists"):
If the box contains a diamond,
I desire to believe that the box contains a diamond;
If the box does not contain a diamond,
I desire to believe that the box does not contain a diamond;
Let me not become attached to beliefs I may not want.
The second principle is "rationalists should win" or "Instrumental Rationality". What wins is how we define "rationality", regardless of your preconceived notions. "Rational" techniques that don't win are suspect.
Many subcultures claim to have insights that most of humanity lacks (and some even do). Which of ours are the most important is less clear-cut than the two principles.
I feel that the links in Raising the Sanity Waterline, and also The Fable of the Dragon-Tyrant, and Beyond the Reach of God are especially important and could serve as your "rationalist scriptures", but that's my opinion.
Arguably the LessWrong Wiki is something like your desired compiled list of rationalist wisdom, even if it is old and out of date.
There's the Twelve Virtues (http://yudkowsky.net/rational/virtues/).
I like the religious/mystical language and imagery, but I think it's important to remember that the Sequences/Virtues/Codex/whatever are not scriptures in the traditional sense. Scriptures are unquestioned; they're something you're supposed to take on faith without disagreeing. Somewhere in the Sequences, Yudkowsky explicitly says that you're not supposed to blindly listen to him, and at least implies that he's probably made mistakes in the book.
pointing curious people to 1000+ page books is daunting.
Then don't read, say, Rationality A-Z as one book - break it up a little. According to RAZ, that they are like 6 books: https://www.readthesequences.com/
Related, has anyone compiled a list of "Rationalist Wisdom"? Like a bunch of sayings that distill Rationalism down that we can point newbs to?
Writing is a skill; you can't simply decide to do it and automatically do it well, even if you believe it is an important thing to do. I hope that in future, some people with sufficiently high writing skills will become rationalists, and one of them will prioritize making simple accessible rationality materials for beginners.
More precisely, writing is more than one skill. I mean, Eliezer definitely is good at writing -- the success of HPMoR is an evidence for that -- and yet it's his Sequences that people complain about. Seemingly, "good at blogging" and "good at writing fiction" doesn't imply "good at writing textbooks for beginners". So it's the person good at writing textbooks for beginners we are waiting for, to join the rationality community and produce the textbooks.
I understand that the title sounds like an oxymoron, however, we it seems like we do have scriptures. The Codex, HPMOR, Rationality A-Z, etc are basically required reading so that we can have a community with a fixed starting point, however they don't seem to be well compiled.
HPMOR is a complete story. The Codex and Rationality A-Z are two series of blog posts so they retread a lot of territory - has anyone tried to edit them into more coherent books?
Related, has anyone compiled a list of "Rationalist Wisdom"? Like a bunch of sayings that distill Rationalism down that we can point newbs to? I ask because I was looking for a list and couldn't find one, and pointing curious people to 1000+ page books is daunting.