Newer iOS devices and macbooks can send MIDI over Bluetooth LE (low energy).
Details available here.
Thus a MIDI chain could be created like this:
1) AUUG Motion Synth ←(via Wi-Fi)→ iPad
2) AUUG Motion Synth ←(via Wi-Fi)→ iPod touch or iPad ←(via iRig MIDI)→ hardware synth
Manufacturers are also looking to make wireless MIDI connections much easier than this however, with products like:
The AUUG Motion Synth app uses the AppleMIDI protocol (sometimes also referred to as core MIDI). This is an adaptation of RTP-MIDI, which is designed make MIDI more reliable and effective over wireless networks. Thus, to be compatible, any receiver must be able to parse this specific MIDI protocol.
Ad hoc networks between iOS devices can get 'drowned-out' by mobile phone signals in live venues. The bigger the crowd the bigger this problem becomes.
We have not tested this solution ourselves, but it might be possible to cable-connect two iOS devices together with this product: