I don't feel like they are doing this the proper justice it deserves in terms of story (which is what the series is known for). I feel like it's just, hey here is all your favorite characters. Go fight and stuff.
There should have been a big story build up and the epic CG that we know can be pulled off thanks to the FFXIV realm reborn cutscenes.
It's been too long since i played the original PSP version, I think they TRIED to do that but its just not great execution.
They're showing off the gameplay rather than cutscenes because that's what arcade players care about most.
The PS4 port (which is a year away at minimum) is where they'd add any story if they're going to bother with it.
Sure there are many characters that can be added to Dissidia and would make people happy about it. This is actually one of the few instances where DLC would be perfectly justifiable...but instead SE will just release Dissidia Revenge in two years to add Noctis, Shadow Lord and some new villain from FFXIV 4.0.
They confirmed months ago that they'll be adding new characters in updates. They're aiming for 50+ in total.
If it's anything like the Gundam VS games (since the gameplay is pretty much identical at least), they'll continue adding new characters to the arcade even after the port is released, and the console version will get them a couple of months later as DLC.
Then we'll get Dissidia Revenge, with all the DLC from the first game included in the base game, and that'll get it's own set of DLC.