Sega registered a trademark for what appears to be the title of the next PoPoLoCrois game, “Narcia’s Tears and the Fairy’s Flute” (“Narcia no Namida to Yousei no Fue “in Japanese). [Thanks, @keke_094.]
The trademark, which was registered on July 24, doesn’t mention PoPoLoCrois by name, but the name “Narcia” is likely that of the forest faerie Narcia, the main heroine of the series.
PoPoLoCrois Story developer Epics put up a staff recruitment add back in June looking for staff to handle UI designs for smartphone/console games, 2D and 3D graphic designs and effects.
A new PoPoLoCrois smartphone game was also expected to be announced in January of this year, but we haven’t seen or heard anything about it since around October 2016. Perhaps this will be changing sometime in the near future.