I also agree with adding the instruments

There was plenty of hard work put into the instruments on PC (graphics and sounds by noto and Omni) and migration over to iDevice should not be too difficult. Instead of keyboard keys to play notes you could do a touch-based keyboard much like GarageBand and the million other music apps :3.
Methinks this would be a great addition to iEra!
Ahead of time I would suggest adding an option to mute individual players because I can only imagine the horrid dissonance of at least 40-something people playing at the same time in the start location. Perhaps an option to mute all players' instruments(in case some people don't want to hear instruments at all) and then provide the option to unmute players on an individual basis via their profiles.