idutils complex formula query support
Coccinelle has had support for glimpse for a while now, and it had proven to yield the best performance. Although glimpse is open sourced now (official repo here, repo that builds here), the software is not well maintained. Coccinelle also supports GNU idutils and this seems to provide very good performance. For optimal performance Coccinelle could be extended to support idutil's regexps, but another alternative is to use complex forumlas similar to what glimpse supports.
For details refer to this thread.
mkdir idutils cd idutils /usr/lib/git/git-cvsimport -d:pserver:firstname.lastname@example.org:/sources/idutils idutils
Other desired features
The biggest feature that is desirable for now is support to query using complex forumas: using a combination conjuctions or disjunctions (and's and or's). Other than this though, other desirable features: