It works in Paris. Those who want to just leave will leave despite having store access.
Those who want to shop will do so anyway. And do so via exiting on MSUSA.
Regarding the decor, so long as any additions are period it will be a nicely dressed corridor. They don't want people stopping, pausing to take photos, crossing the pathway. It is an exit route for the masses so they can get to the monorail line quicker
Any un themed back walls visible will be bad show. Things need to be hidden. But period advertising, again like MSUSA of DLP and proper lamposts to fit the theme should suffice to create an extension of and connect the Victorian gardens of the hub and Town Square.
Anything less though will be poor.
This also, Ironically, improves the guest experience with shopping. Anyone who's ever wanted to grab just "one more" item on the way out of the MK and has been caught in those insane crowds knows that. There's a fine line between the kinetic excitement that causes people to spend their money on Main Street and the stress, confusion, chaos, and "where-the-bleep-is-my-kid" atmosphere when the crowds are so big. Also, from a retail loss prevention (i.e. shoplifting) point of view, this crowd is a nightmare. My guess is that Disney will come out very much ahead in dollars and guest satisfaction with this new arrangement. There is NOTHING at WDW more stressful and chaotic than getting from the MK to your chosen mode of transportation after the parade or fireworks.
They've been working on this for years. We were there 5 years ago in July and we were herded out through that back entrance. I was shocked that they would open up their back stage to guests (we only got a bunch of cast members with mini light saber airport tarmac red flashlights to guide us along). I was also relieved. At the end of our journey we were surveyed about it. We said we would welcome this arrangement but didn't like seeing all of the trucks and dumpsters along the way.