Looks like Taro’s Search in forum feature was implemented since (remember to add IMPLEMENTED in front of it in the list).
I’d like to add an improvement: make “All words” the default search mode, instead of “Exact Phrase”. “Exact Phrase” made me miss many threads as I expected it to search individual words by default, as in most search engines. User could switch to Exact Phrase, or use the classic approach of surrounding words with double quotes to force exact match.