If you have a project in mind after the one you are completing now, as I usually do, this could present a problem. The next project could demand to be started; it could cannibalize your present efforts. My rule is not to think too much about future projects, keep them at the level of fantasy. Oftentimes, the next project is not even the next project, but a kind of distracting notion that I should be doing something else, anything else, because I am sick to death of the current project.
My next book was going to be on Antonio Gamoneda. Then it was supposed to be another book on Lorca. Then it was going to be two books, one on performativity in poetry and the other on Spanish modernism. Then the performativity book and the modernism project collapsed into a single book, which has a chapter on Gamoneda from the first book-that-never-was, plus elements from the other three ideas.
Now my next project is nicknamed (for internal use only) Another Damned Lorca Book. I don't yet know whether it is just reflecting my sense that I have more to say about Lorca I cannot fit in What Lorca Knew, or whether it's something I really need to write. In any case, there will be a volume 6 of my complete critical works, but I'm not sure it will be end up being ADLB or not.
Blogging is actually great for generating new ideas and discussing them without actually having to begin them. I will be blogging on Bemsha Swing a good deal about ADLB.