Well, if a regular challenge is what we've been doing, then a mini challenge would have to be quite small, focused, and easy enough to do in one session without expecting a large time investment.
Steve's recent updates to Anim8or haven't necessarily been new features but rather enhancements to what's already there. Also, I figure he's only midway through these enhancements since he has yet to touch the sequence and scene editors. So it'd be hard to do anything practical in terms of focusing a challenge on these enhancements.
I'll post a simple mini challenge and see if there's enough participation to do more.