One of the main things keeping the high street alive is the inflexibility of couriers
Main problem for me with shopping online is that I'm not going to sit at home all day waiting for something if I can help it - so it's still easier for me to pop out to Currys or wander down the high street to buy something if it's bigger than will fit through my post box, or high enough value that the courier wants a signature or can't leave it outside. The moment somebody comes up with a design for secure "dumping boxes" at domestic properties that couriers are happy to leave goods in, the death of the high street will be significantly closer. Perhaps it would be something like a large steel box bolted to the wall, with a 1 use code to open it that you'd type into the couriers website at the point of sale.