Money is no laughing matter so making it a quest sounds fun but if they don't figure it out then you have wasted everyones time and your money would be gone forever. I don't see a problem with including bitcoin in a will though and when I write one I will seriously consider it, I wouldn't even need to keep the private keys anywhere if I left them on an exchange. I'm pretty sure they would have to abide by the rulings of the will anyway.