Describe the workflow you want to enable

Creating third-party packages that offer objects that are meant to be passed to estimators, but which aren't estimators themselves.

Describe your proposed solution

Would be nice if there could be some class similar to BaseEstimator that would offer pretty printing, HTML representations, and so on; but without needing to be an estimator (e.g. without having metadata routing and similar).

This could be used for example as a base class for objects that are meant to be passed as constructor arguments to actual estimators, and which are thus desirable to show with a pretty-printed form when visualizing estimators. For example, something like parameterizable probability distributions offered as objects in third-party packages that are meant to be passed to estimators from said third-party packages.

Describe alternatives you've considered, if relevant

No response

Additional context

No response