That's /slightly/ part of the issue. Creating separate 3D mesh variations for to suit would only be a portion of the issues they'd face.
On top of providing separate gear components to compensate for the leg structure, is the games skeleton.
Currently, every race in the game uses the same skeleton, featuring the same number of joints/bones for each animation, this makes it very easy and streamlined to "add in" new animations for pretty much
anything.
Certain occasions such as the Lalafell Arcanist animations or Roegadyn Warrior/Dragoon animations are different as a result of their body shape, (but this is simply a specific animation they've decided to use for them, not a separate skeleton).
http://people.eku.edu/ritchisong/plantigrade.jpg
As someone who's had to rig/weigh and animate these damned things in the past, digi-grade legs
sometimes require more joints, this is where problems occur.
http://www.somastruct.com/wp-content...ntigrade11.jpg
As you can clearly see, the human joins simply rely on
three main connection points;
Hips,
Knees,
Ankles. (This is all that's needed for basic human leg animation).
As the profile view of the logs leg shows, it relies on
four main connection points;
Hips,
Knees, and
Two Ankle joints.
This creates a problem already. The original plantigrade skeleton will have let's say 42 bones in it, the digigrade one now has 44 bones.
The computer is now confused and can no-longer apply the weights or their influences to the correct joints on the skeleton as two new joints have been added.
(There are some ways around this, but as I said before, FFXIV has a huge focus on animation quality, therefore they'd be likely to fuss over such details)
In terms of animating characters, there
are ways into tricking a normal planti-grade skeleton into the form of a digi-grade one with a little bit of trickery.
However in terms of the quality of animating FFXIV, and the attention to detail they like to go to, they'd essentially have to provide unique animations for this new race, simply based on the leg structure (hence why the new race screenshots have plantigrade legs instead of digigrade.
"Why does this matter?"
It matters because, they're going to sit down in their various teams involved in the creation of this new race, someone is going to say "How about Ronso".
Both the animators and the modelers are immediately going to go
"But here's a list of issues that are going to be caused as a result of using that race"
"Do we have the time to compensate for that?" "Will we be able to find a solution?" "If not, whats the best course of action".
In the end, I couldn't really fault them for sticking with a race that'll suit and fit a human shape/skeleton, to reduce the effort and work-load of the various sub-set teams.