Geez, what about if the engines were on the wings? If there is a crash, I'm sure it will be spitting shrapnel and will make getting out of center area quite dangerous.
Now, if the engines were in the rear, THAT part of the plane is not the safest part of the plane to be, especially in a crash! As someone mentioned, the Sioux City UAL crash hit the rear first with No. 2 engine on top. That part of the plane was really lucky since there was no fuel on that part of the engine. However, the Delta crashes in Dallas(the L-1011 and 727), the pax weren't so lucky with engine No. 2(engine 1, 2, and 3 on the 727!).