For live play the system can be setup so that all the sounds load at boot up (Just like current keyboards) so that there is no lag when changing sounds.
I'm not sure, I guess it would take much too long to load it at boot up, it is probably not a few hundred Megabytes (which took the Korg M3 already 1 minute to load), but a lot of GB. Wouldn't one need a "data streaming" solution like the Kronos or Kurzweil Forte has? I don't think it would be easy for a keyboard to handle this tons of data without latencies.