There are not enough of them.
The answer of course is to PRM fit more 153s etc, sealing up the bog or removing it. The bog is the big cost. TrainFX is cheap (and rubbish) and other stuff is minor, mostly involving the colour of stuff like handrails.
TrainFX is cheap....?
As you say, main things are door sounders, seating spacing, PIS (both visual and audible), external displays, colours and positions of handrails etc. People make a big focus of toilets on here, but the other smaller items have a greater overall impact on passengers with accessibility requirements in my experience. Just to note, it's often hard to tell who would benefit while they're standing on the platform, so it isn't just as simple as 'keep an eye out and put them in the 158 instead' or whatever. If 153s are going to be retained, they absolutely should be modified to be compliant.
