I haven't read the 6th ed rules yet (I know I'm behind the curve, but as I don't have a
FLGS I play at...

), but one thing that comes to mind that would remove this usefulness is poisoned shooting. I play against
DE, and the thought of a dreadnought going down to masses of poisoned glass shards that should simply shatter off the hull doesn't appeal to me. I don't know if the new
MCs are vulnerable to poisoned shooting or not, but if a dread becomes a
MC, it needs a rule to nullify poisoned weapons, or dreads will be useless against armies that take them.