[mjb]

Are you familiar with Joe Hellerstein and Peter Alvaro's work in this space? CALM provides something of a unifying theory of mergeable operations, of which CRDTs are an "object orientated" special case: https://arxiv.org/pdf/1901.01930.pdf

In practice, designers choose coordination-heavy protocols like consensus for a number of reasons. One is because writes don't or can't be merged. Operations as basic as simple assignment (x = 1;) can't be merged, so that's very real. Another is because readers can't tolerate weak consistency, because their business logic needs to make decisions at a particular point in time.

You're right that the thinking behind CRDTs (and CALM) is useful in reasoning through determinism in this context. The determinism problem, though, is easier than the general monotonicity problem, because only determinism is required and not associativity or commutativity.