Starting when I was still a child, I've greatly enjoyed numerous incarnations of high fantasy. However, it has never been my only thematic area of interest. So, when it comes to MMOGs, I've always wanted more variety. Perhaps the ongoing growth of the category's audience signals that such a time is upon us or at least close at hand. Considering how the market is growing and evolving, here are some concepts that seem to hold unrealized potential.
Zombie apocalypse survival
Players live in a world filled with undead (plus possibly other monsters as well) where, since resources aren't readily available, they must decide who their friends and enemies are. What's more, these roles can shift as circumstances change. Obviously, this idea has become increasingly prominent over the last few years, principally due to the huge success of The Walking Dead TV series. However, the more general concept of a post-apocalyptic zombie survival MMOG has been around quite a while longer, at least a decade now. At this level, it's certainly easy to imagine a compelling game.
Yes, I'm well aware that some attempts have already been made to implement this theme. However, we've yet to see any of them become particularly popular. I think a key reason, albeit not the only one, was simply timing. Basically, the market is, of course, substantially larger now than it was a decade or even a few years ago. But that's not all. In addition, I believe its desire for and willingness to embrace a zombie apocalypse survival MMOG has been growing over time. So, this particular barrier to successful entry has at least partially dropped.
So it's clear, I'm not suggesting there's a huge audience waiting to embrace something bad or even mediocre. Indeed, I hope this will never happen for any type of game. That said, I think it would be great if we've arrived at a stage in the evolution of the MMOG genre where more projects will be conceived, started and released that step outside the “safe” realm of fantasy (and to a lesser extent, science fiction).
Accordingly, I'm somewhat disappointed that the upcoming H1Z1 hasn't generated broader buzz. It does seem to me that the fans of SOE's game tend to be highly interested in it. What I wonder about is why there aren't more of them. Maybe it's the IP. For what it's worth, I suspect The Walking Dead Online would have greater pull, possibly quite a lot more depending on the publisher, developer, etc.
Vampires vs. werewolves
This concept is also far from new. Like the previous one, it's listed because I think the time and market conditions are or soon will be suitable for an MMOG based on it to become a solid hit. There's clearly no shortage of interest in vampire-themed movies, TV series, books et al. Some have even managed to generate considerable revenue despite less than favorable critical reactions. That said, I'm not about to suggest there's so much pent-up market demand that anything at all will fly.
However, I do believe that a well-made vampire vs. werewolves MMOG could be pretty successful. Unlike the case with zombies, there isn't a particular IP that stands out for me. However, if having a known one would be beneficial, I've seen people saying they'd like to see quite a few, from Twilight to Blade, Buffy / Angel, True Blood and more. To my mind, each of these has at least a couple of meaningful faults or obstacles to work around. On the other hand, none strikes me as completely impossible to adapt.
At the conceptual level where I don't have to assign much weight to possible or even likely implementation issues, this theme has definite appeal. Both of the supernatural species are cool, with diverse but highly intriguing types of abilities and powers, albeit not a lot of them. Because vampires and werewolves already have a well-established adversarial relationship, it would feel completely seamless to incorporate a PvP element. Guilds would also fit in very naturally.
Adventurer / explorer
What I'm imagining here is a game with an Indiana Jones- or Lara Croft-like vibe. I'll grant that the highly character-centric nature of these specific properties may be challenging enough to rule them out. That said, I don't see myself as a designer. As a result, I can list this concept because it's one that I regard as having market potential if someone far more creative than I am can figure out how to build an MMOG upon it. I believe there's enough talent within the development industry that it can be done, especially if more designers are afforded the opportunity to think outside the fantasy / science fiction box.
Such an MMOG might well have to be a theme park. These days, it's fashionable and thus common in some quarters to regard this type of design as a problem. For me, however, it's not inherently better or worse. If a game is well-made and fun to play, I'm not bothered if it constantly holds my hand, directs me where to go and tells me what to do next. How much I enjoy it is paramount.
If you can't stand theme park designs, that's fine for you. I'm not trying to get you to change your mind. Nowadays, a game can do pretty well by capturing a relatively small share of the total MMOG market. If this is accomplished by ignoring certain segments, so be it. I suspect a solid game based on adventuring, exploring, solving mysteries and puzzles, etc., both singly and in groups, might find a surprisingly sizable audience.