In a new interview with Famitsu magazine, Bravely Second producer Tomoya Asano has already begun the planning stages of the third installment in the series:

浅野「このタイミングで言うのも何だが、私の中ではすでに『ブレイブリーサード』の構想がある。本作の売れ行きが良ければすぐに企画書を提出する予定。応援よろしくお願いします」

You might say "what" at the timing [of this annoucement] but there is already a concept for Bravely Third inside my head. If sales for this title [Bravely Second] are good, then I plan on submitting a proposal immediately. Please give me your support.

Hopefully Bravely Second sells well enough to warrant those ideas in Asano's mind.