Ask HN: What would happen if most of the money was in index funds?

So Warren Buffett has been telling laypeople to put their money in index funds in every Berkshire Hathaway annual report I've ever read. As I understand it, the allocation of funds in such an investment strategy is primarily influenced by the activities of actively managed investment funds. How would index funds work if they had a majority of the money? Or a supermajority? What if they had all of it?