Too slow? The start/finish straight is fast, and the jump section is very fast aswell, with a propper tuned rallycross car that track would be too fast for the normal rallycross standards
Rally or rallycross? We don't have any rally tracks in LFS, so wishing for longer ones doesn't make sense.
LFS doing rally properly isn't likely (or even possible?!), would take too much time, and it's not a real multiplayer form of racing (rallying). RBR is old and ugly but still 50% better than what LFS rally could ever be.
Rallycross then, well the tracks we have now are long enough. With proper rallycross cars the tracks would be too fast to race on. If anything, any new rallycross tracks should be slower (with the current cars), twistier and generally a better design.