There sort of is on the actual speedrun.com rules. It bans emulator tools and tool assisted emulator features - you could make a strong argument that run-ahead is a tool assisted emulator feature since it utilizes save-states to predict what inputs you’re going to press.

Tool-assisted emulator features such as save-states, re-recording, or frame advance are not allowed.

Has there ever been a ruling on allowing run-ahead mode? I’ve read some forums that don’t allow it, others than don’t mention it.