Always had an idea since Splatoon 1 for a map that takes place in the middle of a subway station. Called is Angler Station.
The spawns would be located at the subway entrance and you descend down the stairs/escalators into the main area. The central area is a square sandbox style in layout, similar to MakoMart. The main gimmick of the match would be the two lowered train rails running horizontally through the map. Normally they're safe to be in, as well as being inkable terrain, but every minute on the minute two trains will zoom through splatting anybody in their way and making the area completely inaccessible for about 10 seconds, a warning prompt and visible indicators will appear 10 seconds in advance. During this time, the only way past the trains are grated walkways that go over them.