This is essentially what being asked in https://github.com/Dev25/mcrouter_exporter/issues/9
mcrouter offers memcached shard metrics, for example:
[..] STAT 10.64.0.81:11211:ascii:plain:notcompressed-1000 avg_latency_us:344.766 pending_reqs:0 inflight_reqs:0 avg_retrans_ratio:0 max_retrans_ratio:0 min_retrans_ratio:0 up:5; deleted:108046 touched:869669 found:1951422718 notfound:66660413 notstored:1825893 stored:51096164 exists:19914 timeout:183 remote_error:70 [..]
The info provided are more related to mcrouter itself rather than a high level breakdown of the memcached operations (get/set/cas/etc..) but it would be useful in my opinion to have per shard/server metrics rather than relying only on aggregates.