Recently, Compile Heart had a big reveal of several titles, among them was the next Neptunia title, CyberDimension Online. If you are trying to wrack your brain on how a Neptunia title would translate into an online game; don't. The game won't be online at all, but rather, is about the Neptunia goddesses playing an online game, where you will play their avatars, similar to how the .hack series and Sword Art Online was portrayed (and knowing Neptunia, probably some gags stabbing at both of the aforementioned series). Neptunia fans are likely already familiar with the fictional online game that Vert plays called Four Goddesses Online, and this will be the game that the group will be playing (the Japanese in the game's title translates to "Four Goddesses Online"), though Vert is reportedly not the main character this time. This is according to the previous week's Dengeki Playstation issue, which was detailed a few days later in a Siliconera post.
This time, Neptune and her friends are portrayed in more of an orthodox fantasy setting, where the goddesses' characters will have appropriately orthodox fantasy designs. So far, it seems that Neptune will be playing a "Holy Knight" of sorts, Noire a "Dark Knight", Blanc will play a "Priest", and Vert will play an "Enchanter". The game's genre is stated to be an action RPG, meaning it will probably play a bit similar to other Neptunia action titles Hyperdimension Neptunia U: Action Unleashed and the more recently released (in Japan) Megatagmension Blanc + Neptune vs Zombies with more RPG flair.
Reportedly, the story is that while playing Four Goddess Online, Neptune and her friends begin noticing new characters appearing in the game, and fight against hostile ones, including one that will be similar to one of the Neptunia series' main antagonists, Arfoire.
The character designs are done by the Neptunia series' veteran designer, Tsunako. The game is reportedly 20-30% complete, hinting at a possible Japan release date of Winter 2016, but there is no solid date as of this writing nor anything for a western release.https://www.youtube.com/watch?v=ww4QotA2htI
If your craving for Neptunia needs to be sated, the PS Vita bound Megatagmension Blanc + Neptune vs Zombies will be coming out on May 10th in the US and May 13th in the EU. Hyperdevotion Noire: Goddess Black Heart will be hitting Steam on April 26th.