The question of consensus and mutability are, to some extent, separable; immutable data does not provide liveness without consensus guarantees. See, for instance, Datomic's design, where a strong coordinator is needed to serialize updates to otherwise immutable/replayable state.
Indeed. Although the use of confluent data structures where possible combined with immutable data stores combined and 'live' functional reactive programming across device boundaries -would- drastically simplify cases like these.
