They do do it in Singapore, and always for a waypoint on descent - ANNOYINGLY!
The problem is that RTA works very well for a waypoint in cruise, but
NOT for a descent waypoint, VNAV PATH is in sole control in this phase. (At least for Boeing aircraft, I cannot speak for Airbus).
Also in Singapore, it appears to be beyond ATC's capabilities to advise of a RETA when 45 minutes or so from destination when you could do something about it. I think that Singapore ATC must have shares in the sub-contractor building speed brakes.
Regards,
Old Smokey