Spend say £500M (USD/GBP/EUR) on experts, per annum.
Imagine typing a search and getting a response: "Give us 30 mins to respond - here's a token, come back at 17:35 with your token" ... and then you get an answer from an expert, which also gets indexed.
The clever bit decides when to defer to an expert instead of returning answers from the index.
I'll leave the finer details out.