Mikko Koppanen has posted about some updates he's making to the PECL memcached extension, more specifically around binary protocol support.
There are quite a few things still missing and only binary protocol is supported at the moment, but the code seems to work reasonably well in small-scale testing. I am not sure whether this is useful for anyone, but at least it allows things such as quick prototyping of network servers, exposing sqlite database over memcached protocol etc.
An example of code using this new functionality is included in the post showing how to create both a simple sever with attached "get" and "set" handlers and a client to connect to it and enable the binary protocol.
The code is still work in progress but it's available in github: https://github.com/mkoppanen/php-memcached/tree/feature-server. Note that you need to compile libmemcached with -enable-libmemcachedprotocol and the PECL memcached extension with -enable-memcached-protocol.