Well, to go along with the Ultimate Jungle Hunter I can think of a few things they might do with Big Chap.
The cowl on the head could do with some improvement. The Gorilla Alien they issued actually came with two that you could swap out, and they actually fit right and stayed fairly well. Every Big Chap I've gotten has had a warped head dome that didn't sit right. So that's one.
So, give it the ultimate paint treatment, give it swappable head cowls. So you can either have a clear or a foggy one. Maybe a set of new hands that are in a closed position. Maybe include an egg and/or hugger/burster and a display stand.
That would make it "ultimate" in my view.