We did have a prototype that opened to the rear, but frankly it would not close up as tightly as the front open version and, therefore, was more vulnerable to rain penetration. The front opening bag mimics our panniers and closes snugly with no need for inside flaps to help keep water out.
Of course the point of having a rear-opening bag is that it makes accessing the main compartment simpler while you’re in the saddle. However, the Orpington is still very accessible from the saddle. Because it has a single front and center attachment point, it was easy to lift one side of the lid and reach into the bag to retrieve items from the main compartment.
I’ve been using the Orpington for over a year and I’ve done this maneuver many times. In fact, I have even unlatched the buckle up front, and opened and closed the bag with my right hand while riding. I would not recommend that technique, particularly since lifting the edge of the lid is pretty effective.
For now we don’t plan to make a rear opening front bag. However, if you want the rear-opening bag there are plenty of great bag makers out there doing quality front rando-style bags that open toward the rider. At the end of the day, it’s your happiness that matters!