It doesn't have to be 90-seconds-with-a-robot easy for a replacement at 6-8 years. At likely costs for the replacement battery, a few hours of technician time on top of that won't make much of a difference.

Also, I don't think that battery lifetimes can be stated with such certainty yet. Few electric cars have been running long enough to know just how the batteries age with that usage. About the closest available is the fleet of older Priuses that are hitting a decade or more on the road, and they seem to have occasional failures but not the consistent aging that's been predicted... but of course they use the battery completely differently, and capacity is less important.