Like other's have said. If your user interface relies on key-up, it's not really possible in general. A given linux machine may only have a serial console, and afaik, you're not getting key up from any serial terminals; certainly not any common terminals. It's just not part of the design, and short of a time machine, it's unlikely to become part of the design because DEC isn't around to update the spec for vtXXX terminals or their implementations.