Custom logs logs_xml.config is a good candidate to convert to Lua bindings. I'm thinking that we bind fairly directly to the internal logging objects so that conceptually it is the same but instead of using XML to construct objects, you use Lua. We would just construct Lua states on the fly to evaluate the file.
This is the last usage of XML and would let us nuke proxy/shared/InkXml.* as well as our dependencies on expat+libxml2.