The problem is that most probably a trustless decentralized system cannot be efficient enough to work as a medium of exchange. You need to make some concessions on one or on the other side. Bitcoin stays trustless and decentralized — but not efficient. It can thus work as digital gold, but not digital cash. There can be a second layer over Bitcoin (Lightning for example) that would be efficient enough to be medium of exchange — it could be still quite trustless (with some timing complications) — but less decentralized. In a way this would work like gold and currencies based on gold.

Then you can also have DPOS currencies — which probably can be efficient enough — but much less decentralized, because they rely on a small set of efficient servers. There can be ways to make it reasonably trustless — but it will not be censorship resistant.