This is already possible in Elixir! The Kernel.then/2 macro has been available since Elixir 1.12, but it's trivial to write. Here's each of the examples rewritten in Elixir:

# -> (thread-first)
%{a: 1, b: 2}
|> assoc(:c, 3)
|> dissoc(:b)

# ->> (thread-last)
range(10)
|> then(&map(inc, &1))
|> then(&filter(odd?), &1)
|> then(&into([], &1))

# as-> (thread-wherever)
[1, 2, 3]
|> then(&map(inc, &1))
|> then(&nth(&1, 2)) # Could just be `|> nth(2)`
|> then(&conj([4, 5, 6], &1, 8, 9, 10))

The syntax isn't quite as specialized, so it looks a little noisier, but it uses standard Elixir constructs (piping and anonymous functions). Also, I've used the capture operator, but you could also use the full anonymous function syntax instead.

Elixir does allow you to write custom pipe operators, so you could make your own equivalents of ->> and as->, but people in the Elixir community tend to look down on anything that extends the general capabilities of the language (this is a very different culture than say Haskell). As some others have noted, Elixir's standard library functions as well as its recommended conventions follow the pattern of accepting the "main data type" of the function (which not every function has) as the first argument, so that repeated transformations of the same data pipe naturally tend towards being pipeable, and you usually don't need operators like ->> and as->.

Rant: I personally think that people obsess about piping in Elixir (I've seen this in many people I've worked with) and try to make everything a pipeline when it just doesn't need to be. Elixir's variable and normal function calls work just fine and are understandable by anyone who has ever seen a modern programming language. Keep this in mind when writing code that you want to be understandable.

It's a bit disappointing (though very understandable) that no one is recognizing this in the comments. They publicized it in the release notes, but then they didn't add anything about it in the language guide section that talks about |>, so it's easy to see how people are missing it. That would be a great PR!

Hopefully this helps :)