This is nice! I hope a lot of people get involved in this! I know I go to the gym 4x a week for the past month or so, and plan on continuing that.
Also, crunches / any type of situp is TERRIBLE for your back. My coach who just finished up his master's program on personal fitness readjusted our core workouts after (XC) practice to the extent where we never did any form of crunches, sit-ups or anything that closely resembled them due to his research and what he was taught.
So just be aware of this, if possible, you may want to do some sort of alternative on the crunches days for the core challenge!
Can't wait to see how many people get involved with this though