There are a few misc thing floating around about a new allied race for the Tau. The rumors state that these units will not be available right away, which means we will see some converting going on upon release if the rumor holds true. The second little snippet is a rumor with some concept pics displaying a Vespid Heavy (or something close to).
These are rumors, so please take with a grain of salt.
We have another snippet from Ghost about the other new alien race who don't look like they'll be appearing at release; Not Zoats (despite them coming back to WFB in Storm of Magic) but they may be 6-limbed.
via Ghost21
one of those is close to the vespid heavy