I like your idea Arkive, but as lolig said, maps take a ton of blocks. Even more, it's very hard to know beforehand how many blocks a map has, and there's probably nothing more tedious than opening a map in the editor to count the number of blocks it has ( 'w')
I think it could be done as a "building in a budget" type of deal, within a copper count instead of a block count. Makes more sense and it's easier to check.
As for Lolig's idea, it's pretty cool but that sounds more like a 2 month contest. It's already hard enough to make a single route within the alloted time, imagine a second one and hiding it xD I'll keep this one in mind for next summer tho.
On sonixerik's idea I feel as if it'd yield very similar maps. The average MTC has a 90 second max for the tracks, and tracks are generally around half of that. The sequence you are talking about would take around 7 seconds to drive in valley and quite possibly longer on canyon or stadium (since you can't just change your direction in those envis). Locking 20 seconds of a track that most likely will be under 50.
In general, themes that can be read as "you are forced into this section multiple times" end in a lot of the same, because driving flow doesn't always allow for said combinations so you have to force them in, and then you can't have them consecutively or the map's boring...