some of the custom maps made in halo are realy awsome and with the parkour aspect of Brink community made custom maps could be realy awsome

This would be a fantastic additon, much more exciting than the current promised DLC's additional maps and and characters. I would create a vertical map in which SMART could be used for something more than hopping over a ledge or climbing up a stair-shaped stack of crates.

I would imagine players are given the choice to produce either an upper-Ark or lower-Ark map. They would have full control over structure placement and map boundaries. They would also select what objectives will be performed and in what order. Setting up objective points, determining the time, or choosing a path for a bot would be up to the player. I would also like to customize other rules such as what weapons, classes, and body types may be used.

Nah man. Second you start limiting a players choice of his play style youre gonna lose people. Like the map editor idea tho.