It's a framework extension point - different than an API which is something my business logic invokes and, as a user, I would likely learn to use on a daily basis.

I don't expect users to make new datastore dialects on a daily basis.. nor I expect my business code to invoke a or have compile time dependencies on the datastore signature.

I guess it becomes more of a grey area when considering the FQCN is to be mentioned in configuration files, but as you say we provide short-hand names. If a (power) user implements his own datastore, which is the case in which I expect him to type his FQCN directly in the configuration, he will use the package name he prefers.