I'm not sure if this was ever confirmed by a riot dev, but very early on I was led to believe that each new map would have some sort of gimmick or new feature of sorts that didn't exist in other/previously released maps. The list is as follows(to the best of my knowledge)

Haven - 3 bomb sites
Bind - Teleporters
Split - Vertical ziplines (first time)
Ascent - Doors with switches (first time)
Icebox - Horizontal zipline (on A site)
Breeze - Dropdown chute / solid metal switch door
Fracture - 4 Ult orbs / attackers access to opposing sides of the map / underground access
Pearl - ?

As far as I can tell, the tiny sewer crouch-entry to defense spawn is the only unique thing about this map, but can this really qualify as a gimmick given the competition it has in the other maps? (Fine the breeze chute was kinda lazy, sorry viper mains, have to include mandatory breeze hate)

So this begs the question, has the map development team run out of creative new ideas to drop into maps? Or the more obvious question, have I not noticed something being the dumbass I am.

Before y'all say it's underwater with a train system, please note that all the items listed above are part of gameplay, and not just map/off map decoration.