By now there is autocompletion for
- variables in output channels
- Rules channel (to a certain extent)
- Form channel
I request full autocompletion for the contents of the CMS_HEADER area. Looking up the options of the navigation CMS_FUNCTION is annoying and any enterprise CMS with a built-in editor should offer autocompletion to its developers. Thinking forward, this is a requirement for distributed template development in external IDEs.