I don’t think Apple plans to restrict anything but its own .ibooks format. But that doesn’t matter because, as Mike Ash puts it, “Unless we’re friends, your intentions don’t matter to me at all, only your actions.” Apple isn’t anyone’s friend but Apple’s, and its actions so far are to reserve a broad swath of rights pertaining to everything iBooks Author is capable of “generating” (whatever that means).
Even if we’re right and Apple doesn’t care about PDFs or plain text files, that’s still the Apple of today. The Apple of 20 years from now might turn out to be a completely different company, and this EULA has no expiration date. That’s a dangerous situation for authors and publishers who care about long-term distribution rights. It would be best for Apple to clarify the terms now — and, I hope, loosen them — rather than prolong the uncertainty.
Source: venomous porridge