The first limiting factor would be the hydraulic tappets that 20VTs have. As rpm rises, the oil would get pumped out of them until the valves cease to open. However the limit for this is still pretty high - over 8000 rpm.
However, whether the rpm limiter
needs to be that high is a different matter! The actual limit I would set the limiter at would depend on what rpm the engine makes peak power. I would usually set the limiter anywhere up to 7.5k depending on the engine spec and it's intended use. Maybe more, just depends