All my 1/4 Alien maquettes had no EX version. But I agree, an EX version with an extra goody would be awesome! Black goo canister or a severed David head would be really cool.
If he is in 1/4, he's gonna be huge! Big Chap is 28" tall already and I believe an Engineer should be even taller. Although, I still think Big Chap looks more like 1/3 than 1/4 scale when compared to the other 1/4 Aliens (excluding the Dog).