Why dont you go one step further and offer shared NoSQL instances - for instance, Redis - which can pretty much double up for what memcached does.. but also so much more.
One step even further would be, people can spin up on-demand instances of whichever NoSQL server they need - Cassandra, Voldemort, Redis, Riak... you name it.
Hi, well, that's a nice idea that I thought also. But the thing is, I'm full time somewhere ! Lets see if this Linode limited one works, and if there is a demand I will surely think seriously about it.
edit: just to be clear, I'm not offering one instance of memcached per person. It's only one instance for all.
One step even further would be, people can spin up on-demand instances of whichever NoSQL server they need - Cassandra, Voldemort, Redis, Riak... you name it.