They are closer to 50% accurate (coin flip) than to 100%. I don't get what you mean by "more accurate than what we have today" -- we have SAT and ASVAB today. Colleges use a multitude of admissions criteria specifically because there is no single test that can predict collegiate success. Some schools have actually dropped the SAT requirement because it is not a reliable indicator.The SAT gives you an idea on whether the taker has the potential to succeed in college. The ASVAB gives you an idea if the person can succeed in the basic training courses for some MOS or ratings. You can look at what makes up each area that they use to gauge your chance of success.
Neither are 100 percent accurate, but they damn sure are more accurate than what we have today.
Do you mean financial success? While there is some correlation, it's well-known that IQ has a very low R-squared; that is, IQ score accounts for only a small fraction of the enormous variability of personal incomes. If I told you that person A has an IQ of 135 and person B an IQ of 95, and nothing else, you won't be able to predict who is more financially successful. To emphasize the lack of predictive power of IQ, consider how your predictions would change if I said that person A is a black female and person B a white male. Would they change again if the high-IQ black female lived in San Francisco, while the low-IQ white male lived in North Dakota?The monkey in the room, IQ, is the best measurement of success potential, according to psychometricians.
Success -- financial or otherwise -- is a product of many hundreds of factors. Trying to predict it with a single factor is like trying to predict the weather a year from now solely by looking at the current temperature.