Note the Go implementation is effectively halted due to frustrations largely stemming from questionable choices in message layout and incompatibilities arising from JS (un)marshalling oddities that are largely hidden by the single implementation (it's easy to be compatible with yourself).
I would not classify SSB as "simple" to implement in anything but JS.
Well, the lack of a specification is a major hurdle. IMO, some of the glaring issues of the protocol could have been caught early if there had been an attempt to formalize the protocol.
That said, hindsight is 20/20, and I don't doubt there'll be some work to write a specification once the idea stabilizes somewhat, but since the current version of the protocol has been adopted by users, I think updates to it will be challenging.
