This is a good idea.
I've mentioned elsewhere the irony between the UK Editions using the same tile for both
Falling Block and
Blocked Squares despite the fact that the rules handle the two differently, but the US rules introduced 2 different tiles, despite the fact that the rules were changed for the US Edition so that both
Falling Block and
Blocked Squares were treated exactly the same so no differentiation was needed.
I too have a
Dead Fall Trap that causing rocks to fall from the ceiling/roof causing 2CD of damage (no defend), but doesn't leave any 'residue' but I think that could be enhanced by the inclusion of a
Rubble Tile (that also could be used for other occurrences of rubble outside of a trap situation.)
Sadly for me personally I won't be implementing this as I don't have the US Edition, so don't have the tiles

That said, for my
1. Keep the
Falling Block Trap exactly as it is but use the
Blocked Square Tile 2. Introduce a new trap type
Dead Fall Trap (technically this isn't new as it is covered in one of the GS Quests already just with the same name as the
Falling Block Trap) but have that result in 2CD damage and a
Rubble Tile being placed potentially under the Hero. For me
Falling Block and
Falling Rocks is a bit too similar and may cause confusion.
3.
Falling Block Tile renamed as a
Rubble Tile, which don't block movement or sight, but do cost an extra point of movement (but I would specify this extra point is used when you move off a
Rubble Tile rather than onto it*)
*The reasons for making it cost an extra point of movement to MOVE OFF a
Rubble Tile rather than MOVE ONTO, it avoids the situation when you are adjacent to a
Rubble Tile with only 1 movement point remaining and you have to lose that point, it could happen that your movement is only 1 so you can't step off but as the vast majority of the time movement is 2D6 therefore min of 2, that is very unlikely. Also making it MOVE OFF means it will affect the Hero who sprung the trap and had the tile placed under him, which MOVE ONTO won't.
4. I would also suggest that combat whilst you are on a
rubble tile, takes place with a reduction of 1 AD/DD (like a Pit Trap)
I wouldn't bother with the optional Helmet rule, HQ generally assumes all armour covers everywhere to keep things simple, so as a
Falling Block ignores armour (and helmets) I would do the same for the new
Dead Fall Trap