It removes the “hope intelligent life evolves fast enough”.

If it was only Uraniam, then you need U-235. That has a half life of about 700M years. Cut in half 2 more times, and there’s almost none left. So if intelligent life took another 1.5B years to develop on Earth (which it easily could have), then that path is cut off.

With Thorium, the sun would probably expand to a red giant first.