I think this is a very good idea and hopefully it will be successful. Yes it's a shame to lose any 'wave down a train' stations but I guess times move on. The two concerns I have really for this system versus the current one is a failsafe, but this will be worked out as part of the trial and possibly adapted, and how early some people may have to get to a station. That would also be worked out and sorted in the trial, I trust it will work and someone will keep an eye on it.
If proven successful, I wonder if some more stations could become request stops where currently, it isn't viable for it to be a request stop with a 'wave the train down' but if it was a button system, it would be viable. Perhaps evenings when things are quieter, introduce the button request on some stations with lower usage. Currently it wouldn't work because a driver wouldn't see a passenger such time they are basically stopped, they might as well stop. Button request of course means drivers are notified and may pass through at line speed if they aren't notified of a passenger thus speeding up the journey.