Optimising `-flattenMap:` would be the best course of action, but you can never optimise away the fact it adds a layer of wrapping things in signals and subscribing to those signals to unwrap them.

Could you try rewriting `-map:` so that it doesn't use `-flattenMap:`?

The performance improvement will not be as good for the single KVO use case, but the improvement will affect any use of `-map:` and operators using it (of which there are many).