[SECProto]

Subway stations in many systems around the world are accessible. It doesn't take much for a minimum viable product - drop a 5m diameter tube for a single elevator from street level down to platform level, put separate ticket gates on it. Impact on surface infrastructure is much less than that 5m. Retrofit it in a few stations a year over the next couple decades.

Your take seems rather shallow. Accessible infrastructure includes curb cuts (originally designed for wheelchairs, also make sidewalks useable by the elderly, strollers, etc who have issues with a 6" step), audible crossing signals (meant for visually impaired, also alert those who are looking at their phones), bike lanes (meant for cyclists, improve the conditions for pedestrians and residents too), .... The list goes on and on where minor improvements in infrastructure design create massive improvements in public spaces.