All very good points and my suggestion is mostly in line with those points.
In most decentralized systems there are no incentives (other than wanting privacy, etc) and I agree with you that this lack of incentives has a bad effect on the quality.
In many ways my suggestion is to create a base layer that is run on centralized servers (like ISPs are centralized, without lock-in) and they have an incentive to make it better because the content-creating users pay them.
So the suggestion is to have a new horizontal market that enables distributed developers to create applications on top of.
The examples of services (chat / reddit etc) could be written on top of this horizontal market layer where the basic data communication part is paid-for and well maintained and the developers will have much less work to make their decentralized systems ready for mass consumption.