Whilst I appreciate the coastline is long there are enough settlements, holiday marine traffic, GA and other populations that something should have been found.
Not likely, even south of Mandurah I would be surprised, let alone going up past Yanchep, virtually no hope.
In the context of the MH370 event I would imagine authorities would have been inundated with every piece that the beachcombers/general public couldn't positively identify as NOT being related to MH370!
Again, not likely, for general Jo public unless its obvious, its MH370 what? More than a week after the event they have lost interest.