I like this idea. Splitting the characters gives poor ol' J.J. a reason to get playtime. It might also be more appealing to some new runners to learn the levels with J.J. and then see if they wanna dip their toe into running with Jeff. I certainly had a rough time jumping straight into Jeff and learning the levels on top of the crazy physics he has.

I think these changes make sense but labeling them as JJ (easy) and Jeff (hard) sounds better than just easy/hard.