Apparently the IRS has not yet published the instructions for Form 1040 for the tax year 2019 yet (as of January 7, 2020). When I go to the standard form instruction index page it just lists the instructions for the 2018 1040.
Since the instructions have crucial year-sensitive information, like tax tables, does this mean I should wait to file my 1040 until the instructions become available?
Tax filing doesn't open this year until January 27, which is "when the tax agency will begin accepting and processing 2019 tax year returns". I assume you could mail in your return before that date, but nothing would be done with it until then. Also if you really want to get a head start, note that you can find draft 2019 instructions for Form 1040, although it clearly says "Caution: DRAFT—NOT FOR FILING".
Yes, you should definitely wait until after the final instructions for the form you're using are released before attempting to file.
In addition to what Craig W said about tax filing not being open yet, using a previous year or draft instructions instead of the final instructions could lead to an incorrect filing. As you mentioned, the tax tables will be different, but there are lots of other things that change from one year to the next, too, whether due to Congress changing the tax law or just normal annual adjustments for various thresholds that are built into the existing laws (including the tax brackets themselves!)
You can file right now. But here's the sucky part: After the final instructions come out, you'll have to re-figure your taxes. Well, almost. And if any changes did occur, you will have to file a Form 1040X to amend your taxes.
"Almost?"
There are 3 parts to tax instructions. Statute: the laws as passed by Congress, and published in United States Code (USC). Those laws don't micromanage: they give IRS latitude on the implementation. So IRS issues Regulations, the rules that implement the laws, which IRS writes as part of the Code of Federal Regulations (CFR). And the publications and instructions which the IRS publishes, for J Random Citizen to read. These "dumb down" the USC and CFR's excruciatingly technical and internally referential language, into something a citizen can easily follow.
Changes to both USC and CFR must be published, in the Government's fun little newsletter called the Federal Register. As a result, there is some lead time.
If you are a wizard, and keep yourself apprised of the statute and code changes, you can simply follow them The IRS instructions aren't alowed to contradict USC and CFR, only explain it. So you should be fine.
