I think I already seen some other people requesting for it here, but I doubt Pioneer would ever do the second option soon (to use the display of the mobile with rekordbox mobile), even thinking this would be a GREAT idea.
Maybe that would be even not possible due to the need for XDJ to send the signal back to the mobile device in almost real time with all the current status from the playback.
But for the first one, yes, that would be more possible. A waveform display just like the one that we find in the CDJ 1000s appearing in a firmware update would be a nice to have.