> My quick guess is that no matter how much work goes into Elixir it is not going to replace all the libs written for Erlang, in Erlang - and so basic knowledge of Erlang is still needed to use Elixir to it's full capabilities, even if just for reading Erlang docs.

This is correct.

Syntax wise, you can learn about Elixir and not worry about learning Erlang syntax at all. However Erlang ships with OTP which, as the blog post says, is a design methodology and a set of libraries for building robust systems.

Elixir does not intend to replace OTP (at all). For example, the next Elixir version that will ship in a week contains docs and guides on how to write OTP applications. We explain most of the Erlang API required to do so, but eventually you will want to call OTP modules and read their docs, for example:

http://www.erlang.org/doc/man/application.html

Keep in mind that calling Erlang modules from Elixir is straight-forward and I believe you will find reading the docs too. You mostly need to know how the literals look like, for example:

    What      | Elixir     | Erlang
    atoms     | :foo       | foo
    modules   | Foo        | foo
    variables | foo        | Foo
    tuples    | { 1, 2 }   | { 1, 2 }
    lists     | [1, 2]     | [1, 2]
    binaries  | << 1, 2 >> | << 1, 2 >>

You can find more information in the Elixir/Erlang crash course:

http://elixir-lang.org/crash-course.html