It’d be pretty hard to estimate a streamer’s income based on hype train history (you only get the one most recent train, not a full history), but sure. Okay. Make it so that hype train status is only available if the hype train is active or in cooldown, or if you have broadcaster permission. That would be reasonable. But active hype trains are public information.
If the data is being surfaced for the front end, it should be surfaced for the API. Information that is available unauthenticated does NOT belong to the streamer - it belongs to everyone.