Hold up, theres a difference between modding and map modding and I think some people might be getting confused (me). In fact I wasn't specific in my reply number 11. I like general mod support as any, which you could download from a third party site to help your UI/whatever.
What I was noting was a demand for a "Map generator/modder" which comes right with the game. What happens then would be sort of like Team Fortress 2: When people make really great maps, the devs use that map as an honorary map. These honorary maps are automatically installed under Impulse.
So Brent what I'm suggesting is that when someone makes a cool map (like the one you suggested ) and people really get into it, and if Gas Powered Games sees so many people playing them, they turn it into an honorary map. Everyone downloads the map and has the option of hosting/joining it.
So Instead of TIME TRIAL RPG being one of the game options to choose, you first choose "HONORARY CUSTOM MAPS" then TIME TRIAL RPG is one of the maps there. If it's really popular then you won't have a hard time finding groups.
And with your arguement that it should come out with release immediately... well I'd like it but unless they'd push the date back they're not going to have enough time. I'm not sure if you were familiar with Team Fortress 2 but they generated a really solid gameplay with map editing abilities, but had a small amount of maps. People did not like that, but with the inclusion of honorary maps there really is a wide variety.
I think that most people will remain attached to the game if map modding comes out immediately with it so that theres a steady stream of good maps coming out. I agree that making other game modes from the get go is useful so here's hoping.