I doubt they will go digital for the next 5-10 years. The profit from digital sales is so small compared to physical CDs especially with their current sales. You can't bulk buy digital songs, you can mass stream like the young KPOP fans but it's not the same. I can see music cards being a substitute for this in case CDs aren't a feasible thing anymore. Have them be a random member music card featuring the one of the senbatsu and include the handshake ticket in the packaging (put it in a colored sleeve so you can't see the member you're getting), you can sell these in more places since they don't take up a lot of space and can be treated as load prepaid cards in the stores.