We already have a configuration via ConfigurableBlock, e.g. DokkaBaseConfiguration.
But for experimental features this approach can have disadvantages:

1. Configuration of such features is not needed for regular users.
2. Too long of a deprecation lifecycle of public API when it is used in the configuration of runners.

Extra options can look like flags, e.g. -XX flags or free arguments in KGP.
Currently, we do not know another case of using such options. This issue might help to explore more cases.