Gollancz is republishing "The Discontinuity Guide" 31 October. The Paul Cornell-Martin Day-Keith Topping text, covering the whole of the classic series up to "Dimensions in Time", will be a yellow-backed ebook, although there's no given price for it yet. Nor is it the only one; three more of their books, covering The Avengers, Star Trek, and The X-Files will also be out that day. The "Classic British Telefantasy Guide" will be along as well, in the future.
Cornell's blogged about the reissue, observing that it includes both introductions from the book's two editions (Terrance Dicks and Lou Anders). He's chatted about it on the latest Radio Free Skaro podcast. Keith Topping's mentioned it in his usual daily new roundup, and Martin Day has put a blog together.
(It's a wee bit odd, since the rerelease haven't been updated, which means that it'll be much the same text that's been serving as the BBC episode guide for lo this many years. Which means they'll probably delete that from the website soon, like the ebooks. Still, it's nice that Gollancz can bring the book to the attention of a new audience.)