Do you want me to go in detail? Okay, fine.
Now, as I understand your wording (and do correct me if I am wrong) is that "the talking body part of Leela" have not yet been revealed and that it will be revealed in "The Mutants Are Revolting" (this summer season's finale). Correct?
So let me quote you this from the very interview you linked:
Craig Ferguson has the most remarkable guest role of the year: He is playing a talking part of Leelaís body. We discover that Leela has a little more to her being a mutant than we knew about.
Craig Ferguson is credited for "Attack of the Killer App". He has made his appearance. I have my doubts he will appear twice this season. I do not recall that ever happening in the history of Futurama. Not even Tom Kenny or Phil Hendrie.
I realise that this have not stopped the writers from reintroducing characters that used to be voiced by guest actors, but in most cases, their reappearances are very short and usually just one liners (with the noticeable exceptions of Dixie and Robot Santa), so without Ferguson, I have my doubts we will ever see the boil again.