Anecdotally, one job in Melbourne about three years ago comprised about 20-30 457 visa developers, and 3-4 local developers. Either there is a huge shortage and we missed the boat on education, or companies are abusing it (imo).
Edit: Where I was going with that last thought: companies weren't happy paying the IT rates they were (which to my mind were less than most trades and most professions, in any case), so they've imported workers that will work for less. Companies still want this, and Turnbull as a result still wants this, so I wouldn't worry about finding a way around it if it becomes an issue.