Have some experience with J, would like to comment.
> A jupyter notebook style ide+repl (maybe a bqn for of RIDE)
J terminal looks pretty close.
> libraries for common scripting tasks
There are phrases (see www.jsoftware.com), but for many tasks it seems not many libraries are actually needed.
> embedding (a la lua) in more languages, maybe even a way to compile to libs so you can call bqn code from other languages
There is a way to call C from J and vice versa; not too convenient maybe... but still quite possible. APL languages don't benefit much from compilation, J interpreter is very fast.
> A jupyter notebook style ide+repl (maybe a bqn for of RIDE)
J terminal looks pretty close.
> libraries for common scripting tasks
There are phrases (see www.jsoftware.com), but for many tasks it seems not many libraries are actually needed.
> embedding (a la lua) in more languages, maybe even a way to compile to libs so you can call bqn code from other languages
There is a way to call C from J and vice versa; not too convenient maybe... but still quite possible. APL languages don't benefit much from compilation, J interpreter is very fast.