A REST call is required to get all valid scenarios for the current customer ID. Currently the scenarios are manually maintained in several ini files to be available in the editor backend.

The scenarios are maintained in the file "ezoe_attributes.ini.append.php":

[CustomAttribute_recommendations_scenario]
Name=Scenario
Type=select
Selection[]
Selection[top_clicked]=Top clicked
Selection[top_consumed]=Top consumed
Selection[also_clicked]=Also clicked
Selection[also_clicked_article]=Also clicked article
Selection[also_clicked_article_global]=Also clicked article global
Selection[also_clicked_image]=Also clicked image
Selection[also_clicked_product]=Also clicked product
...

and in the file "ezrecommendation.ini.append.php":

[BackendSettings]
AvailableScenarios[top_clicked]=Top clicked
AvailableScenarios[top_consumed]=Top consumed
AvailableScenarios[also_clicked]=Also clicked
AvailableScenarios[also_clicked_article]=Also clicked article
AvailableScenarios[also_clicked_article_global]=Also clicked article global
AvailableScenarios[also_clicked_image]=Also clicked image
AvailableScenarios[also_clicked_product]=Also clicked product
...

This should be loaded dynamically / on-the-fly without maintainance for new scenarions on eZ side. The REST interface on Yoochoose service side can provide this data as far i know.