I think it should come with a guide that differentiates between users, clients, relays, and protocol.
Like, do those ostriches mean users or clients?

The protocol can be shown as the two-way or one-way vectors, with a special style and color.
Users are behind clients, which connect them to relays. Moreover, there could be private stand-alone relays and clients too.
And any element can be open or closed source, which can be indicated with various colors.
 

 Fair point. If the objective is to have an explicit diagram of The Nostr architecture and possibilities, this illustration needs more detail. 

OTOH, if the objective is to illustrate “what about nostr’s architecture makes it so special?” then less is more.

I’m not actually sure of The @fiatjaf’s intended audience.