My definition of an FFI was simply about fully supporting native threads. Simplifying FFI definitions has not been a big deal for me. It is either a few hours of work, or if more than that, then I simply use Swig.

As for finalizing arbitrary objects, please see http://community.schemewiki.org/?guile-guardian

I agree on the speed part. But guile 2 is getting better. The reason guile cannot be as blazing fast as say gambitc is their need to inter-operate with all sorts of C code. Native threading included.