Neat plugin. I'll have to try it out.

Now we just need to vote with our money to get the author to officially support clang. The code doesn't look too complex at all.

This doesn't necessarily have to be difficult to implement.

You should consider first going the route that vim did.  They allow user pluggable extensions to provide the drop-down list.  There's already a vim-clang extensions to take a peek at if you're interested.