He mentions that he will enable "Multithreading on by default" - isn't that a "very hard thing" that only Hotspot does and Python/OCaml can't because of the GIL?
Multithreading in Common Lisp runtimes has been pretty common for a while. In ECL in particular, it's been there forever: it was already there at the time of the original 1994 paper announcing ECL (http://3e8.org/pub/scheme/doc/lisp-pointers/v8i1/p30-attardi...).
It's "hard", not "very hard". Many high-level language implementations have true threaded parallelism; a GIL is a stop-gap to avoid rebuilding an existing sequential interpreter, but it's not an essential component.
