Diamonds being scare and high-priced is not a problem for DeBeers, no. But it is for most other people who would like cheaper diamond for jewellery or for industrial/consumer uses. Wouldn't you like a iPhone with a screen of solid clear diamond? It would be hard to scratch.
IMHO, DeBeers and the perception of diamonds as scarce and valuable can only stand against engineering progress for a limited time.
The raw material, carbon, is cheaply available. The scarcity is an engineering problem, which is being solved.