I've been working on converting the existing 'unoconv' document conversion functions into a pluggable interface where unoconv is just one of the options. This will allow for a greater selection of conversion mechanisms, and supported file types.
This is still a work-in-progress, but details of the existing changes are available at MDL-55528.
Eric Merrill has also made the suggestion that we additionally support asynchronous conversions and I'll be looking at ways in which we may achieve this shortly.
I'm also hoping to look into additional converters though I cannot guarantee that these will be part of the inclusion into core.