I've done published research where we started by using data from a gravitational lensing search for black holes, and used data they had collected but disregarded on very distant stars. A mere 100 years ago, there was not an astronomer on Earth who could have conceived of gravitational lensing. My point is not necessarily that we will make even more ambitious and unexpected use of gravitational lensing itself, but rather, what will we invent in the next 1,000 years plus that we have no way of concieving of right now?