|You can match completion items by their abbreviation. This works for both camel case and underscore notation.
|The abbreviation expansion engine also allows you to type parts of the words from the abbreviation, making your search more specific in a convenient way.
If you have more suggestions or cases which are not handled well, I'm happy to discuss this further. Have fun hacking!
P.S. If anyone can come up with an efficient algorithm for doing what is depicted in the last image, I'd be interested. The current one is quite slow for some corner cases.