The rules editor in DTM features data elements search suggestions and autocomplete:
Currently it seems that the feature is not available in the condition editor or in the rules editor (although it is possible to select the DEs set using the db icon):
It could be worthy adding that feature.
I see this use case is already listed in the Launch Basic Use Cases and already submitted.https://wiki.corp.adobe.com/display/ACS/Launch+Basics+use+cases
Due to the openness of Launch and these configuration screens being controlled by Extension Developers, we actually don't have the ability to do this system wide. There is a feature request logged to do it for the Core Extension, but that is the only one controlled by the Launch team.