A guide for DD2 could be released shortly after the game, if the Larians can schedule at least month of beta testing after features/quests/maps/etc have been finalized, and they refuse to make significant changes to the game after release based on feedback.
Since it is difficult to estimate how long it will take to write and debug any complex program, and publishers almost always have a say on release dates, there is no guarantee on the beta test length. What is guaranteed is that after release a vocal minority (or majority) will complain about something being changed or something not being changed enough. If the Larians 'fix' this, another group will complain that they liked it the way it was.
Getting a complete accurate guide and getting the game as soon as possible with requested game balances or feature changes are mutually exclusive, even though both are desirable.
