Agree, it will all come. From a replacement standpoint, when newer tech comes from a hardware/physical standpoint should be pretty easy to design to fit into the current battery compartment. Will be a question of how easy it will be to integrate into software as well as all the hardware/software components (ie cooling/battery management). Will be interesting to see how Tesla handles this. Given how all the hardware and software is meshed, along with security and safety concerns, will be surprised if they allow anyone to tinker. But I’m sure people will hack and make it happen.
I think Tesla should offer upgrades in the future. While some debate the need given the proliferation of superchargers, others want it for independence, towing or living in areas with sparse charging options or extreme cold weather. Also if future technologies allow for very rapid charging it would be nice to upgrade. While society has determined that a new car must be purchased every few years, the reason I bought a Tesla is that it can improve with time. The idea of supporting sustainable transport and creating a better earth for our children, can be better attained if the consumerist model is disrupted. I think that change has to start from the industry. By allowing battery or performance upgrades it makes it easier for a percentage of people to increase the duration of ownership. And now with full electric drive trains, the engineering simplicity (relative to ICE) makes this an easier option. The issue that makes this tough, is that this idea is viewed as an opposition to creating profit. Again, this duration of ownership is not for all, and my viewpoint is not meant to look down on those choose to replace cars more frequently. My Tesla is going at least 300,000 miles, or as long as I can keep it running without prohibitive costs.
An even better option would be to offer a conversion for your old battery cells to be used as a powerwall at your home for a nominal packaging cost. Even a 75 kWh pack with degradation to 40 kWh (even at the extreme end) would provide more than enough power for your home with solar).