In the 'Assert Sentence' tool of the Cyc browser, autocomplete is now possible.
Uses YUI3 autocomplete while elsewhere original authors used YUI2.
I thought about updating that stuff but much of it is within compiled java classes (in plain text, so I guess I could do text replacement but it isn't worth the trouble without the original code IMO).
YUI3 has limitation in terms of the delimiter- it can only have one character as the delimiter and that is set to the space character.  As a result a space needs to be placed after parentheses.