It's come to realize that cache store plugins really ought to be extending an abstract base class as well as implementing the interface.
The reason being that should we need to extend the API in the future we cannot do it via the interface. We'd need to optionally support things in order not to break cache store plugins every time we make a change to their API.
As such I'm purposing to sew an abstract base class into core now, it'll be very basic but will allow us to expand in the future much more readily.