Confirmed thru multiple places, at a recent convention in France a new Mysterious Cities of Gold series was announced.

No idea as of yet if it will be a coproduction with Japan like the original, but apparently the designs will be very similiar, and the original series director is involved in some fashion. 3 seasons of 26 episodes each.

Original French Source {I’ve double checked this and confirmed with multiple people whom I trust that this is in fact real}