Meters generally already have a screen for showing remaining time. And the meter would have to be online if you can pay from an app, unless the meter is now just a pole with a sticker and everything including remaining time in in the app (Which is not the case for these meters).
Now that meters are moving from purely mechanical to electronic devices, the extra cost of the display and connectivity can be reduced by having a central pay station for a row of parking spaces. I believe I've seen some form of central pay station on some streets.