I really recommend you do customer discovery here (just like what YC would teach you). Given the number of lifters who are Instagram savvy, I think you might be surprised.

If you do a ipad version, remember you can make it keyboard friendly, so even that reason is out.

I can think of more and more things that are only possible in the mobile version - bar code/QR code scanner (in case you are selling tickets to the event), livestreaming to YouTube/Instagram, etc