I mean, that there's no key up event in tty context goes back to the beginning of time, and is not Linux's fault, and not even Unix's (nor VMS's) fault, or anyone's fault, because this all works the way it does because of how terminals worked, and they worked the way they did because it was simple.

If, in the late 70s, key up events in tty context had been important, then terminal vendors would have developed an escape sequence system for expressing those. But it wasn't, so they didn't.

So, yes, it's absolutely impossible to get key up events in tty context, and at this point it will almost certainly stay that way forever, as it's too late to retrofit terminal emulators, drivers, and applications to understand whatever protocol for communicating key up events. (The right way to do this would be to develop an escape sequence protocol that the tty/pty drivers could decode and turn events into out-of-band events to be delivered via ioctl()s, that way applications that don't care about key up events don't see them and don't need to be modified. But who is going to do all that work?)