That's not chicken feed when there are something like 300 stations with low-level platforms out there, at least a few dozen of which need to maintain compatibility with Sounder, Metra, Metrolink, etc or be completely reconfigured.
Meanwhile we have an appropriation to spend several billion on equipment and no appropriation to spend several billion on platforms, so it seems that serving existing platforms -- whether you do it with a Superliner-height door + inside elevators to reach the upper level or a Viewliner-height door + external elevators to reach the platform.