There are a number of issues with DRL's:
1) The purpose of DRL's are to warn people of your approach (ie you driving towards them)
2) DRL's were considered to be environmentally harmful until LED's came along (that extra half a tea spoon of fuel you use a day multiplied up by the number of cars in Europe = a sh!t ton of CO2)
As such, no requirement for rear DRL as well as something going away from me isn't going to hit me right?
Then you get the DRL at night thing, which is an issue tbh.
I believe that there is another regulation forcing (new) cars to have automatic headlights, which would fix this - assuming that the luddite owner then "doesn't like computers taking over his life" and switch them off.
To the best of my knowledge, there isn't a requirement for rear DRL's now or in the future.
In fact you could argue that in daytime a rear DRL would mask the brake lights...