Well, if the whole place is holograms then everyone falls through stuff.
/s
But uh, let's see...
Let's draw upon mythology for this one. Norse is gone, Egypt is a given, Japanese have an entire archetype (aka Bujins)...
Greco-Roman god based? Zeus/Juno, Hercules/Heracles, etc;?
Or maybe based off of major characters from old classics, similar to what BA did with Dante except with more works? I could totally see Sun Wukong or Odysseus or Mulan as being good things to draw reference off of.
Edit: And Duel Disks already do that in this day and age, given how far the series has progressed. You can even feel a bit of pain from taking a hit and all that. Holograms aren't even necessary for the room itself- duel disks present them on their own.