As some guys said, narrowing down board lists by search result seem good idea.
Although similar function is already equipped as "板内 Bannai" button, it will make search.2ch more convenient.

When no keyword is entered, all boards are shown in the list :
全板
119 消防・救急・防災
21oversea 危ない海外
21oversea2 大人の危ない海外
...and many threads

This is the same as until now.
When a keyword is entered and a search is done, it is narrowed down automatically.
In the list, there are only boards that appear in the total search result.
Then, users can choose boards from it easily.
Some examples by the new function are shown below.

http://search.2ch.net/search?q=%22Let%27s+talk+with%22&;board=&site=&size=10
Key words : "Let's talk with"
Board lists :
全板
accuse 批判要望
dejima dejima
ccc PINKちゃんねる規制議論
english English
entrance ラウンジ
erobbs pink秘密基地
housekeeping PINK削除依頼
operate 運用情報
siberia シベリア超速報

http://search.2ch.net/search?q=%22Let%27s+talk+about%22&;board=&site=&size=10
Keywords : "Let's talk about"
Board lists :
全板
accuse 批判要望
english English