My very earliest memory was 20-21 case files plus BAT which makes 23-24 books. Since he's added Twelve Months, he plans to make it 25 books. Assuming my memory is right, he is doing it because he thinks he needs to work Harry through a lot of stuff and because he wants to step up his writing. I think he wants to stretch his legs and tell either a anthology that happens to all have Harry as POV (maybe Lara or Molly but mostly Harry) or a very introspective, moody story with comparatively little action. I'm excited for this if he does it. I love it when author stretch out because, even if the experimental stuff isn't as good, it usually improves the regular stuff.