Warhammer 40K Tabletop XVII: "Tyranids Don't Have Friends."

[Squark]

Q: Does a model with an Unwieldy weapon Pile In at its normal
Initiative step and then fight at Initiative step 1? (p22/23)
A: No – it Piles In and fights at Initiative step 1.

"With an unwieldy weapon" implies anyone with any unwieldy weapon fights at initiative 1.

Core Rulebook FAQ page 3

Err... That's debatable. Frankly, it's the sort of think that requires yet another FAQ.