Bandai Namco has recently filed a trademark for "Battle Breeders" in Japan. No video game has been announced by Bandai Namco with Battle Breeders anywhere in its name, meaning that this could very well be a brand new property for the company.
It's unknown exactly what kind of game Battle Breeders will be, or if will be a video game at all. As Bandai Namco owns Digimon, it could be a new title in the franchise, or perhaps a spin-off. If not, it's unlikely Battle Breeders will be a new monster-based RPG or digital pet franchise, so it may end up being Bandai Namco's answer to Koei Tecmo's Monster Rancher series and become a monster raising simulator. Since Monster Rancher hasn't had a game released since 2011, the market for a new monster raising sim is wide open. Alternatively, it could be a fighting game starring expecting mothers, but that's a little unrealistic.
Everything regarding Battle Breeders right now is pure speculation. Only time will tell what this new trademark will turn out to be.