Here's a depiction of what it will look like according to Martin Smith from MAGIC (marni1971)
Basically, the backstage area used to direct guests out when it's is crazy busy is being lightly themed with greenery, lighting and period billboards and it's main purpose will be to get guests out of the park as quick as possible so that Main Street isn't as congested (and in some cases straight up dangerous).
The idea behind it is similar to Disneyland Paris' Discovery Arcade, however they kind of dropped the ball halfway and decided not to go all out with it and just make it an area that will be used to relieve congestion. This is what DLP's looks like (there's really no comparison):