Add namespace to the keys being stored in the cache to allow MB to run in shared environments sharing the Memcached server with other applications.
This is just about done. CACHE_MANAGER_OPTIONS passes through the 'options' section directly to Cache::Memcached::Fast, which supports a namespace (https://metacpan.org/module/Cache::Memcached::Fast#SYNOPSIS). The only bit that's problematic is WIZARD_MEMCACHED, which should be changed to use Cache::Memcached::Fast and pass all options through.
Yes, I claimed this as well as MBS-2037 so we could define a global prefix once and use it all three/four places in DBDefs along with other shared memcached options (localhost:11211 is the other shared bit in our default file). Cache::Memcached also supports the 'namespace' option, but you're right that it should also be changed to ::Fast