That catch is that it's not just you playing the piece. The Orchestra is performing 12 concertos over 4 days, with only a couple days notice even what pieces they're going to perform. Springing an unfamiliar concerto on them is flirting with disaster.
Sean Chen actually planned on playing a Bartok concerto in the final, then (apparently) switched to the Rach 3 after someone with the orchestra expressed concern about this.