Mixed mode dual engine jets, why we are seeing none of those?

Not sure what's a fitting NG for this.

Being a newbie to the aircraft related scene I've got to ask this:

why we are not seeing any asymmetrical designs in dual engine jets.

Say you have a low bypass turbofan for takeoff (and redundancy) and a
high bypass turbofan
for soaking in the marine scenery at low altitudes (and fuel savings).

Think propeller minus the associated noise.