Not quite sure how much has been discussed publically, but we don't currently have the manpower to handle lots of complicated parts, and it seems that softdep, in its current state, needs the hand of Kirk McKusick to work.
So the current strategy has been to make the moving parts simpler (softdep, scheduler) in order to reduce the amount of bugs, so that hopefully we can make things faster again later once they're rock-solid. (in case you're wondering how softdep might be an issue, for instance there are lots of moving parts in swap, the buffecache, the page zeroer, that tend to run amok unless carefully tended, and until we get a better grasp on this, something akin to softdep is unlikely to come back)
