If Bangladesh can get a lead of 400 (not saying that they will), then Australia will be under tremendous pressure. I still think they might be able to chase that much, but it will be extremely difficult on a day 5 pitch. Australia are used to pressure, but losing a quick couple wickets against the likes of Bangladesh might induce panic, something they haven't felt before.
Australia are in a no-win situation, and Bangladesh are in a no-lose situation. Even if they go on to lose by a massive margin (8 wickets or something), they still have proven that they can compete and everyone was expecting them to lose anyway.
On the other hand, if Australia win, people would just dismiss it as 'Yea, so what?'. But if they lose.........
The cards are all set up for Bangladesh, can they take advantage?