While perhaps not a member of these boards, Foxxy at Passport2Dreams argues quite convincingly that the exposed backside of Main Street not inherently bad design:
In essence, in a carefully designed environment it's acceptable (and even encouraged) to have places where the theme dissolves into nothing, almost like the undefined edges of a dream. Instead of creating sharply-defined borders of what is and isn't a part of the themed world, it implies another layer just out of reach, adding depth and expansiveness to an inherently-limited physical space (like a toned-down version of the "borrowed scenery" philosophy in Japanese gardens)
In an age where WDI details everything to death, gives tortured backstories to each tiny element, and force-feeds all of it to park guests, it's refreshing to think that the original designers gave the audience credit for being able to connect the dots and fill in the blanks themselves. And while there are many such areas in MK where the theme "runs out," they tend to be crafted in such a way that it doesn't attract the eye. Instead it hints at the illusion of another layer, an unseen world beyond the guest-accessible portions of the park
Specifically regarding the backside of Main Street, the path had single-story structures to set an intimate tone for the walkway, and a handful of trees (since removed for the bypass) to distract the eye from the towering wall beyond. Additionally, it was directly opposite Cinderella Castle, which would command the attention of nearly every parkgoer walking by, leaving relatively few who would turn and focus on what was on that side of the path.
That said, that's not the case here. This is the front side of a major attraction, one that will command the attention of guests in the area. And it will have exposed edges popping out from behind the canopy, and the sides will be plainly visible plopped down right next to another iconic structure. This approach to design is not airbrushing the edges of an expansive painting to imply a limitless world; it's putting on a tuxedo t-shirt and saying it got dressed up.