As title says, in the Dashboard/Card YAML editor there is now autocomplete of entity_id items, but not of service calls (and maybe could be even extended to other built-in instructions such as action: ).
This autocomplete feature could be a configuration setting on a global or per-card basis, to allow common built-in actions to always autocomplete, and also for third-party card developers to specify their own autocomplete list.
Example:
tap_action:
action: call-service # does not autocomplete
service: cover.toggle # does not autocomplete
service_data:
entity_id: cover.blinds_bedroom_blinds # autocompletes