A couple open questions:
1 - Is it reasonable to expect a 10x programmer whom your are trying to poach to give up so much time? (Or should you give them a $250 Starbucks gift card or something similar for their time?)
2 - Can you really ferret out cheating? I had a grad school classmate who paid someone to do his (non-programming) take-home homework for a job interview, and he got the job. He only lasted 6 or 7 months, but it was enough to be awful for all parties involved. I don't have a great counter-solution other than ask for someone to come in to the office to do the work, and even then you can't tell if they have remote support.