In terms of total quantity, not ease of access, focusing on scarcity and price.

He's saying that if at some point we develop a way to make it worthwhile to bring large quantities of gold from space, gold could be worth less than wood (or rather, than several other items, especially Bitcoin).

Although there's another issue: if it were profitable to plant trees to collect wood in deserts or even on other planets, the price of wood would also fall considerably.