My take is that EV's are on the same point of the cost/performance cars that PC's were in the 80's and 90's. Back then, PC prices were fairly constant but the performance was improving at a dramatic rate and anything more than a few years old was not very useful, since the software requirements were also increasing and trying to run new software on an old PC was painful or impossible.
My 2017 will still have all the utility I need (gets me around town for near $0 costs). So even if a 2021 Leaf has a 300 mile range and can charge at 100A or whatever, my car will still suit my needs. I don't expect used EV prices to drop as fast as used PC prices used to since they will keep more of their usefulness over time compared to a 1.0 mega-pixel camera or a 286-based PC.
The biggest opposing argument I can see is if someone needs more range or faster charging. If an EV is used as an around town car, that isn't a issue, at least for me or others in smaller metro areas. As long as there is a demand for short range, cheap cars that should support Leaf prices in the future.
Of course, if a miracle occurs and you can buy a 100kWh Leaf equivalent with unlimited battery life for $20k, that would change everything.