It is confirmed that there will be a third opening called Great Days. It will come with an English version and an Instrumental.
It looks like it'll be sung by Karen Aoki and or Daisuke Hasegawa, or it will be just sung by one and the other will cover the English version.
@WB_anime mentions a date too, 10/19, but it's probably the date the CD will be sold.
found @ 325 likes ON 2016-09-09 19:58:31 BY ME.ME