As I said before, the vBulletin file changes are minimal, only 2 (each with one or 3 lines of code added). The rest is handled by the vbHL global.php file. When VB3 is released, we will have a version for it also. So no need to worry about the new VB version.
Since VB is totally diferent, you will have to use the same process for upgrade like you upgrade from VB2. Is up to you if you want to wait until spring time, when is due the first beta for users.