I would like to see a trained Reek. A rhino like mount would just be the best.
http://vignette3.wikia.nocookie.net/swtor/images/2/24/Thrasher.png/revision/latest?cb=20130901142736
http://img3.wikia.nocookie.net/__cb20100428220200/starwars/images/a/aa/Grievousreek.jpg
My next idea is a little out there, but a lot of my guild-mates would like to see a chariot mount. One specific guild-mate really wants a rakghoul chariot, but that is just a little much.