Maintaining a relay is a public service. I’d argue it’s almost impossible to do in a neutral manner, since it has costs to do.
Most businesses that have the resources (compute, bandwidth, and a devops/network engineer with free time) to run one also exist within some jurisdiction where they are ripe for regulatory intervention. A decentralized collective will have trouble agreeing on a central party to maintain the relay, and both will have trouble finding a new place to run the relay if they fail with one setup.
A distributed relay isn’t feasible, as each party that knows the built blocks can steal the MEV, and threshold encryption would add too much delay.
The more relays a builder trusts, the more exposed their MEV opportunities are to theft, so the number of relays will trend towards the minimum viable amount for inclusion. I wouldn’t be surprised if there are at most 2 credibly neutral, high quality relays until we have PBS.