Power Continued - Forcing the player to pay attention
The biggest issue I can see happening with the playerbase in FF14 is that players need to pay closer attention to what they're doing during group battles. Because the battles are so active and because positioning matters in so many different ways at a much faster pace than anything in WoW, I don't know if the average player will be willing to devote that much time, attention, and effort to "play correctly." This isn't so much a slight on the player but more a comment about the current way that similar MMOs handle their content progression. The easiest way to discuss this is by comparing this game to WoW's item level progression.
One thing that has made WoW into a financial success is the addition of the "brainless" Heroics and "Raid-Finder" content. Here, a pickup group made up of a 5 or 25-person formula in which the average item level of each player must equal a certain number. This number indicates various things but more specifically reflects the basic damage abilities of a well-balanced party. The creation of this conscious numerical indicator changed the playing field for WoW and other games like it forever. Essentially, if a group's item level average is lower than the dungeon's required item level, that group cannot win. They simply cannot DPS fast enough to meet the timed damage requirement before the enemies go into "rage mode" (a concept introduced by FF11 thanks to high level end game monster drama).
For example, all players must obtain an item level of 481 or higher to engage in the current "Raid-Finder" raids of WoW 5.3 content. An average item level of 481 or higher indicates that players will be able to do enough damage over time to finish a dungeon, a raid, or a world boss before it becomes invincible. This basically allows Blizzard to be lazy with their design to create new content along a standard power structure. In 5.4, for example, I'm sure the new raids will require a few new scenarios and pre-raids in order to get their power level up to a point where they can successfully tip the balance of the DPS formula to the side of the players.
This slight, but significant difference in design philosophy is a central point where fans may find reason to love FF14 or despise it. Personally, I believe that the lowering bar for raid completion in MMOs and the now increasing difficulty bar in current gen games may indicate that this criticism of mine may end up being a moot point. Another point of contention may be the required use of a controller.