That's nothing like a Stealer. Stealers have feet, not hooves, and rounded heads instead of dinosaur heads. Fluffwise, the Broodlord is as big a Stealer as you get. No, this looks more like the mother of all Hormagaunts. Powerful hind legs, thorax biomorphs. Only thing that's confusing me though, those legs aren't traditional Tyranid evolution style. The feederbeasts haven't had legs like that since 3rd edition and nearly everything on this is screaming out 'retro'. The only sprues it resembles are the 3rd edition Warrior and Gaunt frames. So I'm going to throw this out there. What if it's a scaled-up model of a smaller bug? Everything is saying 'mock-up' so maybe this is just for display and modelling purposes and the real beast is going to a normal scale Nid.