[Switchblade]

I imagine planning starts at least by the halfway mark of the previous series. We usually get our first rumors around June or so, but I know Toei does some focus group testing early on in the process to help narrow down what they think will be a marketable gimmick for the year. That part is usually settled around the time that the actual production staff is gathered (I remember Gaim's writer being a bit flustered once he found out that the show was going to be fruit-based).

I doubt there's anything concrete about Ghost's successor just yet, but I'm sure some of the basic planning is already well underway.