How about a sprint track/s; it'd be great for online and with a time attack submittable styled leader board it's be quite a cool idea; could go for a short, long, and reverse styled layout for variety as well...

The other two, I'm sure I'm the millionth person whose asked this (but with a twist) but what about a road inspired (non track styled) hill course sprint; anyone ever played Forza? I'm going for the Fujima Kaido style (though with no walls in some parts so there's actual serious risks)..., Also a rally (dirt/gravel) sprint would be nice, as this game does have rally support though rallying isn't really done on circuits. Rain and Night-time racing would be nice too (so we could actually use the lights); winter would be cool too though I've never liked winter racing much (It don't snow where I'm from ).

Jabba

I support this idea alot but you should also know that hill climbs and touge roads have been suggested sevral times before. It's even got it's own + in the list of previously suggested ideas. Another thing you might find interesting is that you can design layouts on all the tracks to make such sprints you're talking about. Perhaps you should get S2 and check what LFS already provides before posting suggestions, no offence.