Still using Memcache wow.
Mcrouter was the first piece of software I worked on at facebook. It's nice to see that you like it! (Though the only thing that lives on from me is the umbrella protocol)
Balderdash. memcached is actively hostile to modern infrastructure and it's not being actively developed except for routine maintenance.
The first time someone stores an entire data structure in a memcache key is the moment you've lost. Playing "read blob, deserialize, update, serialize, write blob" is just dumb when you can avoid it.
Other moments of great failure with memcached: needing to implement client-side or proxy-based replication, having the memcached process refuse to cache more things because a slabs become broken, the first time your developers don't understand memcached LRU is per-size category and not global, ....
Just Say No to Memcached.
Why gild the lily?
> needing to implement client-side or proxy-based replication
It's best practice to replicate the persistent store for availability, not the cache.
Almost all your other concerns appear to arise out of fundamental misuse. It's a cache, not a panacea to cover up basic design flaws in a primary data store.