silverpill:
simple servers that store and transmit messages, and powerful clients
I think I've heard this idea before and I still don't think I understand it. The problem as I see it is that there are certain use cases that are not feasible to implement in a client. For instance, I don't see how you could implement a Reddit-like social platform with a "simple server" and a "powerful client". You simply could not implement the required sorting algorithms as a client.
I feel that this "simple servers, powerful clients" idea excludes many potential use cases and I fear that this would essentially reduce ActivityPub to some kind of glorified email, or at least make everything but the microblogging use case into a second-class citizen.