3) network and storage load - both follow and mute lists in some cases are exceeding single figure kilobytes in size, this is a problem
Discussion
That's true. Some relays will eventually cut off long mute lists, as well, as they have max-event-size.
half a megabyte is probably typical, but i can see that being reduced
there is also data storage strategies that could at least shrink those long strings of repeating pubkeys down to small, varint references, and existing data stores have compression to reduce such duplication of data but at some point the network is gonna be the big pain point