With MGNLACTIVATION-21 ActivationPage was removed as that implementation would not work with 5.0. Hence we have to port the ui.
I tried to wrap the old Ui with the WrapLegacyPageUIAsMagnoliaAppTask provided by the admininterface-legacy module but that fails during install due to the fact that activation comes before ui-admincentral which in turn creates the apps node to which the legacy app would be added.
As a general rule activation should be installed before any module registering a workspace see info.magnolia.module.delta.SetupModuleRepositoriesTask.subscribeRepository(String), and moving activation after ui-admincentral wouldn't work given that ui-admincentral needs to installed after imaging which in turn registers the imaging workspace. That said, the activation UI should probably move to ui-admincentral or any module coming after it.