Two things for Parameters
I put these together in a single idea because the first would be requirement for the second.
1) Parameter Populated on Extract
This feature would only be available for fields that are in extract data sources, because the domain of possible values only updates when an extract to performed (scheduled,manual,incremental).
Only when creating a parameter from a field, either from the right-click context menu from the field, or in the Edit Parameter dialog, and selecting Add from field, would the option to "Populate on Extract" be available.
This option would link the parameter to the selected field and run a "Clear" and "Add from field" on the parameter each time the extract is refreshed or loaded with more data.
This would only be available for fields that are materialized in the extract, either fields that are in the original data source, or fields that are optimized(calculated fields that are evaluated at the raw record level).
2) Set Parameter Current Value by Action
In order to use this feature, "Populate on Extract" would need to be turned on.
This would be similar to current single select filter actions, but the the selected field could only be a single field that is linked to a parameter that is populated on extract (if the field is populating multiple parameters, the user interface should enable selection of parameter as well).
With this new action type, maybe call it a "Set Parameter" action, would enable a user from the select/hover/menu interaction option to set a parameter current value.
The field that is referenced in the action would need to be actively in use on the worksheet as a dimension (same requirement as the Filter Action).