Grass wouldn't be stupid at all, IMO. You could create any fantasy club circuit you would like, or even kart tracks. for e.g. with some 3rd party program you could "draw" some curves and lines, you set a track width and it generates the track itself for AU. I know this would take a lot of times to make but sure it'd add lots of possibilities to create numerous things.
And the other thing along with this (which would not require this amount of work and time, actually could have been done easily) is a dirt/mud covered (even totally) autocross area from the existing one. That'd add a lot of variety to the rally lovers too without wasting much time. (considering how object oriented programming works) This was suggested a few times already (of course without any success or reply
) by me and from others, but still would love to see this happening one day.
Little modification of one area -> lots of possibilities -> more happy peep -> theoretically more content -> winnage.