Mirko,
Thanks for posting your port of the FFT code. As I say on the documentation page, the reason I held off on the FFT port was mainly because I had no working example to guide me, and I've not ever done FFTs myself. I did see the NLISP work on FFTs later and thought that would be a good place to start when I got around to thinking about FFTs again. So your work is very valuable.
As far as waiting for the ffa transition, it is up to you. Though I've been working steadily on it, it is not close to completion. And, I will be travelling the next couple weeks, so not much is going to happen in the near future anyway.
Keep us posted on further improvements.
Liam