The Lagiacrus has been confirmed to be coming back from Monster Hunter Tri and 3 Ultimate. Which species are back are as yet unknown, and as there are not underwater battles, it shall be interesting to see what they do.
The old school Blangonga, as well as the Shogun Ceanatuar, have also been confirmed to be coming back.
Finally, we have a name for one of the new flagship monsters. The big green dragon is now known as Raizecus.