Clearly it was short-sighted of B&B not to have sketched out the FutureGuy plot points at least somewhat in advance.
That said, they take a bit too much heat, IMO, for not having every detail of the TCW plotline written before the show aired. Plenty of very successful writers (Stephen King, for example) are well into the writing process before they know how things are going to end.
King has said that when he began publishing "The Green Mile" on a chapter-by-chapter basis, he had no idea how it was going to end. Same with the "Dark Tower" novels - even after publishing six volumes, he didn't know how it was going to end until he was basically near the very finish, after 30 years of writing it.
The theory is that too much advance plotting drains a lot of the organic flow from the story that otherwise would derive from the characters as they develop.
So I really don't condemn them for starting the TCW and creating FutureGuy without knowing where it was going - it's a valid writing technique. Unfortunately, because the show suddenly shifted gears, they were forced to pull a sudden finish out of their asses, and it didn't work particularly well (and they certainly deserve criticism for that).