Well, an uncontained failure between engines one and three on the 900 are no different than any other pylon mounted twin engined jets, with any failure debris having to puncture through the fuselage to get to the other side.
Most people don't realise that the centre engine on the 900 and 7X is mounted well aft of the other two. There is a large 'S' duct and nacelle entrance is not where the mid engine is mounted!!!!
Certainly the BAe 146 has had its fair share of contaminated air issues, but the DC10 APU was/could be used in flight to assist pressurization and bleed air to the cabin, so not sure there's much mileage in that argument?