We looked into something along similar lines - not silent disco, but broadcasting live commentary over wifi to be received by a users phone. There are a few solutions out there such as https://www.limeonair.com/ and https://www.lineapp.pro/ which are just a couple that I looked into. The main problem being that depending on the number of users you're expecting, we would have had to spend many thousand of pounds installing a wifi infrastructure that would reliably work with potentially thousands of users simultaneously streaming the data. Most existing venue wifi networks just aren't geared up for this kind of usage. In the end, with all the costs, rigging time required, technical complexities and the enhanced risk that this involves, we decided that an old school FM transmitter/receiver based solution was the answer. Much less to go wrong and can scale to an unlimited number of users without latency or network traffic to worry about - keep it simple! Ben