This is the interesting thing. In theory it is possible to provide an education as good as an oxbridge education at say Newcastle Uni or Swansea Uni so you could bring the level of the non elites up. But it still wouldn't be Oxbridge.
Thirty years later it could be on the same level though. All it takes is sufficiently high quality for a sufficiently long time.
Oxbridge is home of the elite because of reputation to a far greater extent than it is due to superior quality of education. They're one of the oldest universities in the world, of course they're going to be home of the elite. The only way to challenge that is to match their quality and wait for it to kick in. It takes a generation or more, but that's the only way to do it.
McHrozni