I love instant answers by ddg. and with bangs it gets even better. But with so many bangs available sometimes I end up searching directly without knowing that there is a bang available for that search.
Autocomplete for bangs can be very interesting feature in these kind of use cases. Duckduckgo doesn't have search autocomplete but with autocomplete bangs user experience can be imprved IMHO.
When user starts query by "!" a list of bangs will appear below search box with bang's source.
Ex. For ser input 'y' or 'yourdic' YourDictionary bang should appear.
!yd - YourDictionary
For input whois who.is should appear.