Versia actually looks promising with its focus on simplicity, although it seems to be modeled almost too closely against ActivityPub, such that it seems it will have a lot of the same problems as ActivityPub (for instance, it does not solve the problem of changing implementations on the same domain).
Extremely good question, extremely hard to answer 
. I think I mostly agree with all the stuff said in that thread the other day but surely there’s more stuff than that.