Just throwing in my 2¢ here, but I don't think that PC is going to be switching all that soon after the release. I'd say that they are more likely to set up a test forum or something so that the staff can get used to the new system and convert/ make new styles before upgrading the public board. Keep in mind that VB4 is probably not actually due for release until early next year. (yes they've sold pre-orders and are making beta version available for those who did pre-order later this month, but a beta is not suitable for a fantastically active board like this.)
Even though I'm still in the process of a few of my styles, the ones that I make available here will probably have both a 3.8 and a 4.0 version.