As I was in Berlin, I visited a supermarket and at the soda corner I checked the Coca Cola bottles: there are only PET refillable bottles with a deposit.
Like HOD, retail business requires a high performance refillable packaging: the caps are removed by end customer, the bottles are in crate and customer bags, fridges, cars... and finally go back to bottling plant for wash and refill.
Coca Cola, the world's most valuable brand, does not take risk. The refillable process for PET bottles is fully controlled and the bottles are used 8-10 years for 30-50 trips, usually the bottles are sorted out due to bad optical properties. This means also Coca Cola is confident about PET bottle refillable ability.
The PET bottles are fully compatible for refillable application... for soda or water! Considering the Coca Cola Company performance in Germany, I am quiet confident that PET bottle use for HOD business makes sense specially considering that HOD system is more monitored (non spill cap, specific crate, unique place of bottle use, identified customers, dedicated deliveryman...) than retail business!