Currently there exists quite some code for different plugin types
like row or handlers to show a select element to choose a relationship.
Beside from that some custom code might require a second relationship,
which is basically c&p a lot of existing code.
Some examples (there maybe exists more):views_ui_config_item_form, RowPluginBase::buildOptionsForm
I guess it would make sense to introduce a method on the PluginBase which just returns an relationship form element.
Postponed: needs info
9.5
Last updated
Related to the Views in Drupal Core initiative.
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Since there has been no follow up in 11 years wonder if this is still a valid task for D10 and up?
It has been over a year since it was asked if this is still relevant. Since there hasn't been supplied I am closing this issue.
If there is work to do here, then either re-open the issue and add a comment or open a new issue and reference this one.